hybridfree/eevblog-posts huggingface dataset:
Why different pulldown resistors for otherwise identical LED drivers? - Page 1
Forum section: electronics / projects

author: MLXXXp
author_rank: Frequent Contributor
timestamp: January 20, 2024, 11:03:59 pm
content: I was given a magnifying glass LED lamp that had stopped working. It appears that the 6 pin MCU in the controller has failed. I reverse engineered the controller and made a schematic.The lamp has two rings of LEDs, one with "warm" and one with "cool" colour temperature, each driven by a separate MOSFET using PWM from MCU pins. What I find odd is that the pulldown resistor on the MOSFET gate is different for each. Otherwise, the circuits are identical. From measurements, the LED rings are also identical other than different phosphor colours in the LEDs.One pulldown resistor (R13) is 150K and the other (R14) is 10K. I'm wondering why the difference?I'm thinking it's a mistake, with one having the wrong value installed for some reason. If that's the case, what would be the proper intended value?My feeling is that 150K would be sufficient. I think it's only to make sure the MOSFET is off during the time the MCU is powered up and the pins have defaulted to inputs, before the firmware configures them as PWM outputs.The schematic is attached.

author: Benta
author_rank: Super Contributor
timestamp: January 20, 2024, 11:16:19 pm
content: More likely that 10k is correct.150k is way too high to turn off a MOSFET if it's PWM'ed.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: January 20, 2024, 11:20:35 pm
content: Quote from: Benta on January 20, 2024, 11:16:19 pmAs I said, it's only during MCU powerup/reset, when the MCU pins are defaulted as inputs, that the pulldown holds the gate low. Once the pins are configured as PWM outputs they will drive the gates both high and low.

author: Benta
author_rank: Super Contributor
timestamp: January 20, 2024, 11:41:10 pm
content: Quote from: MLXXXp on January 20, 2024, 11:20:35 pmMany MCUs have I/O pullups, often in the 100k region. As you offer no information on this I can't help you further.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: January 21, 2024, 12:13:14 am
content: Quote from: Benta on January 20, 2024, 11:41:10 pmThe MCU is dead and unmarked, so I can't identify it specifically. (I'm going to ask for help on that in a separate post).Generally, if a MCU has pins that have weak pullups (or pulldowns), they can only be enabled when the pin is configured as an input. It make no sense to enable them when the pin is configured as an output, as it would be for PWM, because the drive current capability, and thus the output impedance, is far lower that the pullup or pulldown.Anyway, thank you for offering your insights.
Why do ATX Power Supplies Have So Many Parallel Connections? - Page 1
Forum section: electronics / projects

author: Posh
author_rank: Contributor
timestamp: June 19, 2016, 03:50:29 am
content: Hi all,I've recently been tearing down various ATX PSU's for use in other applications, and after cutting down a few forests worth of wires, I've been wondering why all the parallel connections are needed at all?I understand that the motherboard connectors have multiple pins that need power to be delivered, but why use multiple grounds and power pins in the first place?Surely it would be more economical and 'clean' to simply use less wiring at a thicker gauge if resistance is the issue...Cheers,Posh

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2016, 03:58:25 am
content: To carry the current, nothing more.Check the current capabilities of such a PSU and then try to put all that current down just one of those conductors, sorry it won't happen.Now think of all that current flowing through just one pin of those multi pin connectors, again: won't happen.Further, think of all that current terminating into just one PCB trace: won't happen.They're a computer supply not a BBQ.

author: Phoenix
author_rank: Frequent Contributor
timestamp: June 19, 2016, 05:25:23 am
content: Quote from: Posh on June 19, 2016, 03:50:29 amA lot easier to route, terminate and connect multiple smaller wires to a pcb.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 19, 2016, 06:01:50 am
content: Pretty sure that a loom of smaller wires is also a lot easier to bend and route inside a crammed PC case.
Why do CAN tranceivers need so much current when transmitting dominant bits? - Page 1
Forum section: electronics / projects

author: AndersJ
author_rank: Frequent Contributor
timestamp: March 31, 2017, 02:05:07 am
content: Investigating current demand and bulk capacitance when transmitting,I noticed there is significantly higher current flowing IN to the tranceiverthan what goes out to the bus termination.The datasheet confirms that several tens of mA are used within the tranceiver.Why does the tranceiver need so much current internally when sending a dominant bit?

author: 406dany
author_rank: Contributor
timestamp: March 31, 2017, 03:26:05 am
content: I have see the same effect on a MCP2551i have a big spike on VDD when transmitting bit on CAN bus (or VAN bus)I think it is the result of CAN bus differentiel resistor as i have several Equipment on the bus (but not sure ...

author: Niklas
author_rank: Frequent Contributor
timestamp: March 31, 2017, 09:05:08 am
content: Have you checked the current consumption with and without 60 ohms (120//120) bus termination? A 2V differential signal over a 60 ohm load will give you approx 30 mA of current. In addition to that you also have the capacitive load, <=100pF/node, and the wire harness. Also the topology of the output stage might draw some bias and control current.

author: AndersJ
author_rank: Frequent Contributor
timestamp: March 31, 2017, 09:54:33 am
content: I have checked current consumption with a large termination resistance, 250 Ohms.I have also done this statically, or at least extremely slowly, near DC.My original post is still valid:there is significantly higher current flowing IN to the tranceiverthan what goes out to the bus termination.Also I have checked the device with a thermal camera.When the tranceiver is toggled on/off manually the temperature rises about 10 degrees C within a few seconds.The question remains:Why does it need so much power internally?If there was a heavy bus load or a short, then so be it,but why does this happen when there is practically no load?Its no big deal, expecially since other devices seem to be similar.I'm just curious.

author: Niklas
author_rank: Frequent Contributor
timestamp: March 31, 2017, 02:25:47 pm
content: I would guess that it is related to the biasing and base current to the output drivers. The dominant state is not Vcc or 0V and the outputs also have slope control. More analog than digital CMOS inverter type of output.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 31, 2017, 06:10:23 pm
content: Some internal current mirror logic and control amp sort of stuff would be reasonable, but that shouldn't account for more than a few mA in a competent design.Unfortunately this isn't a question you'll find an answer to, short of a pile of NDAs and anawful lotof schmoozing the manufacturer, or becoming an employee at the manufacturer (again under similar constraints).Tim
Why do Li-ion Batteries die! Testing with 6 digit accuracy. - Page 1
Forum section: electronics / projects

author: firepower
author_rank: Regular Contributor
timestamp: March 21, 2015, 02:04:47 am
content: testing battery Coulomb efficiency to accuracy of 6 digits, allows prediction of cell life.Lecture on Li-ion chemistry and additives, charge rates and temperature.https://youtu.be/pxP0Cu00sZs

author: Fsck
author_rank: Super Contributor
timestamp: March 21, 2015, 02:15:12 am
content: it was phrased as a question so when I entered the thread, I thought you wanted an answer

author: firepower
author_rank: Regular Contributor
timestamp: March 21, 2015, 04:05:22 am
content: Sorry about that , just a great lecture on Li-ion and use of high accuracy 6 digit automatic measuring.Thought that would interest all the guys with the Keithley mulitmeters.

author: bingo600
author_rank: Super Contributor
timestamp: March 21, 2015, 10:35:46 am
content: Quote from: firepower on March 21, 2015, 04:05:22 amDammm I have a 34401A, a 3457A and a 3458AI guess i'm not allowed to watch/BingoWell maybe i am anyway , i also have a K2015

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 21, 2015, 12:54:41 pm
content: 6 digits ofprecision.(runs away)

author: paulie
author_rank: Frequent Contributor
timestamp: March 21, 2015, 01:01:46 pm
content: LOL, that is absolutely the funniest post of the week. And I am hugely sympathetic toward your byline.

author: macboy
author_rank: Super Contributor
timestamp: March 21, 2015, 03:58:01 pm
content: Quote from: Alex Eisenhut on March 21, 2015, 12:54:41 pmActually the 3458 has 6 digits of 24 hour transfer accuracy (0.6 ppm). It has 5.5 digits at one year.I relate though, I too hate when accuracy and precision are confused.

author: electrodacus
author_rank: Super Contributor
timestamp: March 21, 2015, 06:45:00 pm
content: I seen that lecture some time ago.My new Solar BMS is almost good enough to do this sort of tests with the 24bit ADC for current measurement. The voltage is just at 1mV resolution / cell and relative accuracy around 3mV.I will need to see what sort of accuracy I get when is done. It will be anyway more than good enough for the intended purpose
Why do we use transfer function in filters? and How to obtain cut-off frequency? - Page 1
Forum section: electronics / projects

author: Michael George
author_rank: Contributor
timestamp: February 09, 2016, 09:50:06 pm
content: I need to know what the equation of cut-off frequency of third order filter is.I found the transfer function everywhere on the internet:I don't understand Why we don't simply use the cut-off frequency equation? Why do we have to use the transfer function?One more question, How can I get the cut-off frequency form the transfer function?I found the above circuit and its transfer function on Wikipedia:https://en.wikipedia.org/wiki/Butterworth_filterThank you very much,

author: awallin
author_rank: Frequent Contributor
timestamp: February 09, 2016, 10:38:02 pm
content: transfer functions are useful because they completely describe the response of a linear system.roughly stated a sine-wave at the input will be that same sine-wave at the output with possibly a change to the amplitude and phase.for deriving the cut-off frequency you need to study the definition of cut-off frequency!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 10, 2016, 08:40:33 am
content: For a general 3rd order system, there need not be a single, well defined cutoff frequency.For an intentionally well-designed one, there is a tolerance of passband attenuation (where the tolerance is smaller than the cutoff threshold), a cutoff threshold (usually -3dB), and a stopband (of the required attenuation slope).Going from transfer function to cutoff frequency is nontrivial, because you must solve a cubic equation for where it intersects the -3dB point (or whatever the threshold is defined as). There may be one, two or three frequencies where this occurs!Tim

author: bson
author_rank: Unknown
timestamp: February 10, 2016, 10:31:43 am
content: Quote from: Michael George on February 09, 2016, 09:50:06 pmSolve for Vo(s)/Vi(s) = -6dB = 0.5

author: Michael George
author_rank: Contributor
timestamp: February 11, 2016, 10:14:02 am
content: Thank you all very much,

author: TimFox
author_rank: Super Contributor
timestamp: February 11, 2016, 02:41:37 pm
content: A more conventional definition of cut-off is the -3 dB point, where Vout/Vin = 0.707 = SQRT(1/2) and Pout/Pin = 1/2 (for equal impedances).
Why does a 10 MHz reference multiplier PLL use a shelf filter? - Page 1
Forum section: electronics / projects

author: pigrew
author_rank: Frequent Contributor
timestamp: April 23, 2017, 10:04:13 pm
content: I'm trying to understand the design of the external timebase input of the Agilent 33120A waveform generator (perhaps to build a substitute option 001 board). It uses a PLL to multiply the 10 MHz input to become a 40 MHz system clock. I have two questions about its design:Why does the PLL loop filter use a shelf filter instead of a simple low-pass filter?The 33120A reference input is 50 ohms. However, the later models (33220A, 335xxB) all have 1kohm input impedances. In fact, I don't see a pattern for which instruments use 50 ohms and which use 1kohm. Should I prefer 50 ohm or 1kohm inputs? Is it that the 1kohm inputs allow the instruments to be connected together with BNC tee-connectors, while the 50ohm input equipment should be used with a distribution amplifier?The option's schematic is in theoption 001 service manual.The 33120A's service manualis also available.Thanks!EDIT: correct link for service manual.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2017, 02:02:20 am
content: The VCO converts voltage to frequency.Frequency to phase is an implicit (and exact!) integrator.The loop therefore has an integral (1/s in Laplace domain) term, and corresponding 90 degree phase shift, built into it.A pole-zero or lead-lag compensator is therefore needed.Finite DC loop gain is not needed, but they went for R121 anyway I guess.Tim

author: Benta
author_rank: Super Contributor
timestamp: April 24, 2017, 07:01:34 am
content: What Tim said.A type-2 PLL system (0 deg phase difference at lock) needs an integrator in the loop filter.This one is 100% by the book.The relationship between the two resistors sets the damping of the loop, the relationship between cap and resistors set the natural frequency of the loop.

author: Wimberleytech
author_rank: Super Contributor
timestamp: April 24, 2017, 03:36:54 pm
content: Maybe you could help us help you by linking to the proper manual.

author: bson
author_rank: Unknown
timestamp: April 26, 2017, 07:42:06 pm
content: I guess 1k makes it less sensitive to AC vs DC, sinus vs square, voltages, and DC offsets. Frequency standards come with so many different kind of outputs that I'm sure that 50ohm resistor would commonly need replacement. I assume they decided 1k works just as well at 10MHz while providing greater resilience and compatibility.
why does pcb track spacing drastically increase over 3050 metres altitude ? - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: February 08, 2014, 08:56:34 pm
content: I'm looking through a table of trace spacings required for various voltages and notice that at say 300V I need 2.5mm if the altitude is less than 3050m and 12.5mm! if over 3050m. Why is this ?

author: Monkeh
author_rank: Super Contributor
timestamp: February 08, 2014, 08:59:47 pm
content: http://en.wikipedia.org/wiki/Paschen%27s_lawLong story short, breakdown voltage decreases with reduction in pressure until you reach extremely low pressures.

author: scientist
author_rank: Frequent Contributor
timestamp: February 08, 2014, 09:14:32 pm
content: TL;DR Less atmosphere = less air = more like a vacuum tube = more likely to arc between traces. Thus, spacing is increased.Probably shouldn't be an issue if your board is masked, though.

author: Simon
author_rank: Unknown
timestamp: February 09, 2014, 08:45:36 am
content: Well I'm looking at the saturn pcb tool and it is distinguishing between bare copper and conformal coating
Why does this circuit pick up a radio station? - Page 1
Forum section: electronics / projects

author: Fungus
author_rank: Super Contributor
timestamp: July 12, 2017, 10:38:58 pm
content: Can anybody explain it?

author: retrolefty
author_rank: Super Contributor
timestamp: July 12, 2017, 10:47:00 pm
content: Simple diode rectification of RF signal demodulates the AM information.

author: strawberry
author_rank: Super Contributor
timestamp: July 13, 2017, 09:36:07 am
content: Same thing with FM

author: HighVoltage
author_rank: Super Contributor
timestamp: July 13, 2017, 10:09:56 am
content: Building a radio receiver is actually very simple.

author: ocset
author_rank: Super Contributor
timestamp: July 15, 2017, 08:29:04 pm
content: look up "crystal receiver" in google.....youll see how simple a AM radio receiver is.I built a crystal receiver , but i couldnt get it to work till i connected the circuit ground to earth ground.
why does this plate reverb preamp need so much gain? - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: September 22, 2022, 02:27:29 pm
content: The EMT140 plate reverb has tons of gain for the contact microphone preamp, but why? aren't contact microphones piezo discs which don't require as much gain as for example a condenser mic?there are 2 pentode stages that have a gain factor of over 300 each, although with negative feedback, and then another 2 triode stages, one with gain of around 25 and the last drives the output transformer but that has only gain around only 3 if my estimation is correct.the output transformer has a 9:1 ratioI've attached the schematic for the preamp[ Attachment Invalid Or Does Not Exist ]

author: Benta
author_rank: Super Contributor
timestamp: September 22, 2022, 03:06:52 pm
content: The reverb units I remember had dynamic microphone-type sensors (= moving coil) with very limited output.

author: Andy Watson
author_rank: Super Contributor
timestamp: September 22, 2022, 03:47:07 pm
content: Quote from: ELS122 on September 22, 2022, 03:14:24 pmSome of them did use piezo elements - e.g. Vox used record-player pickups for both send and receive. However, they had to tread carefully because there were patents involved.I think it was possibly Hammond - the organ makers - that owned the patents.

author: Wolfram
author_rank: Frequent Contributor
timestamp: September 22, 2022, 03:48:40 pm
content: I'm not generally a fan of replying to a post with a youtube video, but this one answers your question pretty concisely.
Why does this step-down converter have this weird resistor - Page 1
Forum section: electronics / projects

author: Neukyhm
author_rank: Contributor
timestamp: July 06, 2018, 11:19:39 pm
content: Hi everyone, I'm sure that some of you have this step-down converter. Usually the (-) output and the (-) input are shorted in these converters, this is good in order to have a common reference, but this one has that resistor in the middle, no idea why.

author: ataradov
author_rank: Super Contributor
timestamp: July 06, 2018, 11:27:01 pm
content: Looks like a current sense resistor. It is just 50 mOhm, don't worry about it.

author: tsman
author_rank: Frequent Contributor
timestamp: July 06, 2018, 11:28:16 pm
content: It is a current sense shunt resistor as those modules have a constant current feature.

author: Cliff Matthews
author_rank: Unknown
timestamp: July 06, 2018, 11:31:50 pm
content: Quite common to sense current on the low-side.

author: David Hess
author_rank: Super Contributor
timestamp: July 07, 2018, 09:58:25 am
content: Low side current sense must be fun when the user creates a ground loop from input to output. Low side current sense is not common at all for this reason.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 07, 2018, 10:00:02 am
content: A fuse?

author: daqq
author_rank: Super Contributor
timestamp: July 07, 2018, 03:02:59 pm
content: As was said - it's a current sense resistor (shunt resistor) - a small resistor in series between the load and the power supply that allows the controlling circuitry to measure the current going into the load by means of creating a small voltage on the resistor.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 07, 2018, 06:17:45 pm
content: Quote from: David Hess on July 07, 2018, 09:58:25 amIndeed. Unless you can guarantee completely floating grounds in all use cases, it's bound to fail spectacularly with the most seemingly innocuous setups, leaving the user very angry.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 07, 2018, 07:10:49 pm
content: Low side current sensing is very common in cheap Chinese modules.It is OK as long as the SMPS module is the only connection between the power supply and the stuff that is being fed.It is also common to not have a real resistor, but to use a (sometimes "squiggly") PCB trace as a sense resistor.
Why factory RESET comes during memory bootloading ? HW or SW issue ? - Page 1
Forum section: electronics / projects

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: May 02, 2019, 07:45:44 am
content: Hi there,I am working a WIFI module as follows,https://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=73461&utm_source=octopart&utm_medium=compref&utm_campaign=OCTPTEC&utm_term=FCM9000SC-100To activate it, need to download 4 image file like Serial Flash Discoverable Parameter coverage.At the same time I am using a USB to Serial COM port works in 5volt.But, wifi module accepts 3.3v, so I am using TX, RX from USB Serial COM which has 3.3 level also.To maintain 3.3 v for WIFI, an external power supply has used.Not sure, after downloading why factory reset command appears ?For voltage swing ?In Serial terminal error massage says,SETUP: ERROR(ret=9)All services have been stopped.Please reboot or setup again.[PRADA:NVRAM] rebootERRORPTIM is relocated to RETMEM (00184110)RaLIB is relocated to RETMEM (00180810)
Why have TO3 package have higher Tjmax than plastic? - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: October 12, 2018, 07:23:27 am
content: Hi folks,I just wonder why power transistors in TO3 package have commonly Tjmax 200°C while same device in plastic package have just 175°C or even lowerIs it because some thermal expansion issues with epoxy vs metal as TO3 have free space around chip and bond wires to expand and contract ?

author: dzseki
author_rank: Frequent Contributor
timestamp: October 12, 2018, 07:38:00 am
content: It is because the glass transition of the epoxy mold of the plastic transistors, it won't melt down, but pressure may build up in the case which may affect the die's electrical properties adversely.
Why is BLDC Stall Current Changing Over 50% PWM Duty Cycle? - Page 1
Forum section: electronics / projects

author: hakansensoy
author_rank: Newbie
timestamp: October 30, 2019, 11:03:44 am
content: Hello,I am in trouble to drive a BLDC Motor -170W with a 3-phase driver circuit, which is designed by me.My PWM frequency is 40 kHz and I just try to get a graph about the relationship between the stall current (I mean the current with blocked motor shaft) over PWM duty cycle (from %10 to %70)In trapezoidal driving mode; why the stall current is rising linear up to %50 PWM duty cycle and rising exponentially over %50 PWM duty cycle? What difference happening over %50 PWM duty cycle?PWM/Current100 / 0.5A200 / 1A300 / 1.5A400 / 2A500 / 2.5A600 / 4A700 / 15AWhat could be the possible reason for it?Is this normal?Thanks and looking forward to your reply.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 30, 2019, 11:11:47 am
content: Depending on the exact ratings and circuit used, either of the following:1)Transition from DCM to CCM. In DCM, the PWM cycle is short enough so that while the current rises during on-time, the stored energy in the inductance fully discharges during off-time, to zero. Each cycle starts from zero - easy to understand. There is no carryover state.In CCM, the current rise during on-time is more than the current fall during off-time, so the current doesn't reach 0. Instead, current value isstoredfrom the previous cycle. On each cycle, it gets higher and higher.You need currentfeedback, instead of dumb PWM. The feedback can be a simple "terminate the cycle when current limit is reached", or a PI control loop controlling the PWM value, based on current measurement. Either way, it uses actual current measurement, hence understand the already stored energy.2)Saturation of the motor inductance. When the current increases, the effective inductance drops. After a certain point, the inductance drops very quickly. This means, the same on-time will cause much higher current rise, if the current is already high.--Stalling the rotor exposes the winding inductance because the back-EMF voltage is simply zero. The circuit can be analyzed as a typical buck converter.

author: hakansensoy
author_rank: Newbie
timestamp: October 30, 2019, 11:20:53 am
content: Thaks for your reply.2) My motor's phase to phase L is 0.0843mHphase to phase R is 0.209 ohm.to=L/R=0.4msAnd my PWM freq is 40kHz and one PWM duty cycle time is 25us.I think there is no saturation.1) I will try the dumb PWM and write it here.Thanks a lot.
Why is EPROM programming voltage critical? - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: November 08, 2023, 09:39:30 am
content: An EPROM might be specified as having a programming voltage of 12.75V +/- 0.25V. What is going on inside an EPROM to necessitate such a narrow range of acceptable programming voltage?

author: moffy
author_rank: Super Contributor
timestamp: November 08, 2023, 09:57:02 am
content: Normally there is an oxide layer on the gate that charge has to be injected through by electron tunneling so the voltage needs to be high enough for enough electrons to tunnel through without breaking down the very thin oxide layer. Also consider variations in thickness of the layer due to process variations and you end up with a moderately precise voltage range.P.S. One would also like to keep programming time down, so that means a higher voltage but shorter programming pulse.

author: CaptDon
author_rank: Super Contributor
timestamp: November 08, 2023, 03:28:44 pm
content: Some of the old 25 volt and later 21 volt VPP stuff had feeble transient clamp diodes on the programming voltage rail and they would fail dead short especially if you hit a 21 volt part with 25 volts. Some of the 12.75 volt stuff seems to have undervoltage lockout where they fail to program at all if the 12.75 is low. The manufacturer guarantees a 'data retention time' and that is hugely effected by programming voltage. You can surely go outside the limits but at your own risk.

author: David Hess
author_rank: Super Contributor
timestamp: November 11, 2023, 01:32:41 am
content: Intel's Flash memory had a warning about ringing on the programming supply which would likely destroy the part. Just a couple of volts high is a real risk even if it is transient.
why is my guitar pickup not picking up the mids here? - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: December 19, 2019, 08:49:26 pm
content: so I used a coil and a sweep generator to test my pickup's frequency response because it sounded like "life-less" when I pluged it in an amp.and I saw this weird graph, I was imagining a drop off at the end like all pickups have cause of the capacitance, but what's weird is that there was a major low-spot at the middle, at around 140hz,I set the sweep generator to speed from 1hz to 16k, maybe it is caused by my phone because I used a online sweep generator, or maybe the coil itself,also the high spot at around 50hz is probably the mains, I will try to input a higher gain signal for a higher signal to noise ratio and post the result here.[ Attachment Invalid Or Does Not Exist ]

author: Electro Detective
author_rank: Super Contributor
timestamp: December 19, 2019, 09:07:12 pm
content: If it's a humbucking dual coil pickup, and has about 5 or 6 colored leads, it may be miswired to the switch, pots and caps,or have an internal wire short or broken wire in the pickup itself.Also if the pickup has been dismantled in the past, the magnet/s may be flipped the wrong way upon re-assembly.Either of the above cancels the lower to mid frequencies.Worst case, one of the coils may be dead or half gone, or faulty from manufacture and never tested before shipping.Good luck

author: Electro Detective
author_rank: Super Contributor
timestamp: December 21, 2019, 09:07:55 am
content: Not sure if we are on the same page matebut..afaik guitar signals sit somewhere between way above microphone and just below home hi-fi and pro line levelsA guitar amp has the proper input impedance and active gain structure to cater for itThat said, if you plugged a properly wired pickup powered guitar into a stereo system, the low frequencies will be good but the highs not so, they tend to roll off
Why is there a series diode with a halogen bulb? - Page 1
Forum section: electronics / projects

author: Jeroen3
author_rank: Super Contributor
timestamp: December 23, 2018, 09:16:45 pm
content: In the process of investigating the possibilities of increasing the light in the trunk of my Honda, I pulled the lighting socket.I've bought an exact copy of this unit, to sacrifice as connector for the LED's I'm intending to mount in the trunk.However, something got my attention, and I can't think of a reason for it being there.Why is there a series diode with the small 5W halogen bulb?

author: james_s
author_rank: Super Contributor
timestamp: December 23, 2018, 10:48:22 pm
content: It's common with mains powered halogen lamps to drop the voltage enabling a shorter thicker filament. For an automotive light though I suspect it may be part of a multiplexing scheme with the various door switches and dome lights.

author: soldar
author_rank: Super Contributor
timestamp: December 23, 2018, 10:55:28 pm
content: It could be that they are using a standard 12 V bulb and the voltage drop in the diode protects it somewhat from the car's higher voltage.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 23, 2018, 10:55:38 pm
content: Is it possible to unplug only the bulb from the whole connector&diode assembly?If yes, then my guess is the diode is there to protect a LED bulb against reverse voltages in case one decides to replace the incandescent light bulb with LEDs. Some LEDs are very sensitive to reverse voltage. Just a guess.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 23, 2018, 11:03:18 pm
content: It's behind a 7.5A fuse branched directly from the 100A.It's low side switched by the trunk door switch.The low side does share some controller input to detect the door is open.Voltage drop wouldn't make sense, since this is the only light I could find that uses a diode. The ceiling lights for example, do not.The LED replacement could make sense. But none of non-indicator lights are LED in this 2009 model.
Why is there noise at DAC mid-way crossing? - Page 1
Forum section: electronics / projects

author: sebmadgwick
author_rank: Regular Contributor
timestamp: May 06, 2017, 02:06:42 am
content: I have found that the Microchip MCP4921 12-bit DAC outputs a small voltage spike (~1 us width) when it crosses half of it's full scale range (code value 2047). This is best demonstrated by having the DAC output a triangle wave using code values 2047 +/- 10, and then comparing this to the same code values shifted up or down by 11 so as to avoid the code value 2047. This is what is shown by the two attached screen shots.Is this a known phenomenon?It does not seem to be mentioned in the device datasheet.I am using the DAC to generate audio waveforms and I had chosen half of the full-scale range as the zero line for the these waveforms. For very low amplitude waveforms, the spike noise dominates and results in a 'square wave sound'. The obvious workaround would be to offset my zero line so that the spike noise is only present in waveforms of higher amplitudes.Is this a common workaround for this problem?

author: rs20
author_rank: Super Contributor
timestamp: May 06, 2017, 02:18:28 am
content: It is mentioned in thedatasheet; on page 3: "Major Code Transition Glitch": 45 nV*s, "1 LSB change around major carry (0111...1111 to 1000...0000)".To be fair, the recommended applications are "Set Point or Offset Trimming", "Sensor Calibration", etc. I've used it extensively with no issues, but I've always used it for setting current limits etc, it's always had that flavour of being not designed for audio applications. So either,a) Minimize the gain after the DAC so that any noise is minimized (i.e., you shouldn't have a massive gain after a DAC which is operating nowhere near its output limits), orb) Use a more suitable DAC.

author: sebmadgwick
author_rank: Regular Contributor
timestamp: May 06, 2017, 02:41:00 am
content: Thanks for pointing that out. Now I have the key words "major code transition" I can see this is described in many DAC data sheets.

author: mikerj
author_rank: Super Contributor
timestamp: May 06, 2017, 02:37:09 pm
content: Suitable low pass filtering should attenuate the glitch considerably.Note that many of these relatively low performance DACs built into micros are actually constructed as two (or more) consecutive string DACs to minimise the amount of silicon area required. e.g. a 12 bit DAC could be an 8 bit DAC followed by a 4 bit DAC. This means you tend to get a larger glitch whenever a code change means both DACs values have to change. In the hypothetical 8bit/4bit combination this would be every 16 counts.
Why is this 555 timer getting stuck ? - Page 1
Forum section: electronics / projects

author: MathWizard
author_rank: Super Contributor
timestamp: February 13, 2021, 02:21:09 am
content: I made a dual tone alarm type circuit for in a wire finder/toner/tracer, with a NE556 timer. A main freq of about 1700Hz and a long freq of about 0.33Hz. I added an LED that blinks with the 0.33Hz part.And on the breadboard it worked ok for a few days, and never had it lock up. But a proto-board, from time to time, the LED gets stuck on. I thought maybe it was current from the other 1/2 circuit, and added a diode, but it's still happening, so it's the 1st output getting stuck high.But then I can turn it off, let C1 discharge to zero, turn it back on, and it can get imediatly stuck on again ?? But wait a few minutes, and it seems to be normal again. For a minute anyways, I just watched C1 ramped up , get stuck there for a while, then cycle 2-3 times, and now it still stuck high.The other side remains normal, ticking away at 1900HZ atm. But now only hear just that tone.This time I wasn't touching it at all, I thought it was related to me flicking an output switch, or moving wires.

author: daveatol
author_rank: Regular Contributor
timestamp: February 13, 2021, 10:29:06 pm
content: If it's not oscillating, I'd check connections on pins 2, 6, and 7, as well as R1, R2 and C1. The circuit, as drawn, looks fine to me, so the issue would be in your wiring.Do you have a photo of your circuit on the protoboard?

author: MathWizard
author_rank: Super Contributor
timestamp: February 14, 2021, 12:36:03 am
content: No photo, but yeah the sim works too. I'll have closer look at the soldering.

author: Renate
author_rank: Super Contributor
timestamp: February 14, 2021, 02:31:16 am
content: C1 is probably leaky.Jumper another 100k across R2 (as a test).
why is this error in this arduino program? - Page 1
Forum section: electronics / projects

author: rizlesz2000
author_rank: Contributor
timestamp: October 18, 2023, 09:35:33 am
content: So in this program It actually uses a SSD1306 oled library. But when i change it to the sh1106 library, it shows me this errorC:\Users\sonid\OneDrive\Documents\Arduino\libraries\Adafruit_SH1106-master\Adafruit_SH1106.cpp:29:10: fatal error: avr/pgmspace.h: No such file or directory#include <avr/pgmspace.h>^~~~~~~~~~~~~~~~compilation terminated.exit status 1Compilation error: exit status 1and in this program if we enable bluetooth library and its functions, The bluetooth option appear on the project. but when i did that it showed me other errorsyes, im using ESP32C3 xiao

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 18, 2023, 01:55:27 pm
content: avr/pgmspace.h is an AVR8 CPU specific header file. It seems you're trying to use a library written for, or configured for, an AVR-based Arudino. ESP32 is not AVR.Ed: oh, merge withhttps://www.eevblog.com/forum/beginners/why-is-this-error-in-this-arduino-program-397458/msg5120301/#msg5120301pleaseTim

author: Simon
author_rank: Unknown
timestamp: October 18, 2023, 05:35:51 pm
content: Please don't double post, you annoy everyone and then get banned.
Why is this MOSFET here? - Page 1
Forum section: electronics / projects

author: Gelf54
author_rank: Contributor
timestamp: October 04, 2019, 09:30:56 pm
content: I've just fixed my old Dell C600 laptop (after our cat decided to mark it as his own, which corroded away some IC pins) and noticed in the circuit diagrams this MOSFET circuit. I've seen similar before and haven't figured out why it's used.It can't be providing reverse voltage protection, since the body diode only has a Vsd of around 0.7V, and it can't be providing under-voltage lockout, since the Vgs threshold is only around 1.7V.Thoughts? Never mind, I think I just figured it out.The 33K & 100K resistors do provide an under-voltage lockout of around 7V I'd estimate.Not sure why this is necessary. The battery is around 14.8VDC. Guess it prevents spurious logic signals before the +5V & +3.3V rails have stabilised, or during power down.

author: Gelf54
author_rank: Contributor
timestamp: October 04, 2019, 09:41:20 pm
content: Because of the MOSFET body diode.

author: Zero999
author_rank: Super Contributor
timestamp: October 04, 2019, 10:31:57 pm
content: Are you sure it's drawn correctly?

author: Gelf54
author_rank: Contributor
timestamp: October 05, 2019, 04:26:33 am
content: I have no reason to think otherwise atm. Is there a slightly different circuit that you have in mind?

author: JackJones
author_rank: Regular Contributor
timestamp: October 05, 2019, 05:20:01 am
content: It looks like a soft start circuit rather than polarity protection.

author: Gelf54
author_rank: Contributor
timestamp: October 05, 2019, 06:27:53 am
content: That's about a 15mS time constant, isn't it, 0.47uF & 33K ?Maybe it's to delay past any initial power-on ripple from the external power brick?

author: Gelf54
author_rank: Contributor
timestamp: October 05, 2019, 08:35:02 am
content: Good to know! Thanks.

author: sanwal209
author_rank: Regular Contributor
timestamp: October 15, 2019, 08:58:09 am
content: It is an In rush control circuit.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 15, 2019, 10:19:43 am
content: Quote from: blueskull on October 05, 2019, 05:40:31 amI feel your pain - I made the exact same mistake about a week ago...
Why is this SMPS controller so expensive? - Page 1
Forum section: electronics / projects

author: AcHmed99
author_rank: Contributor
timestamp: January 30, 2016, 12:57:27 am
content: I was looking for another controller similiar to the TPS40210 only with an integrated switch 50-60V and I found this.http://canada.newark.com/linear-technology/lt8302mps8e-pbf/isolated-flyback-converter-12/dp/18X4340I can make 5 or 6 complete flybacks with the TPS40210 for just what the controller cost. I've been using the TI part and its nice, internal LDO operates off a 52V rail, soft start and internal slope compensation. Anyone know of a similiar part with an internal switch?For comparsion I've been getting the TI part in low quantities for anywhere from a buck and change to 2 bucks and change over the years.

author: janekm
author_rank: Unknown
timestamp: January 30, 2016, 01:31:40 am
content: TPS40210 isn't for isolated applications. This chip is clearly designed for some very specific, probably medical / comms applications where for whatever reason it's attractive to not use an optocoupler for the feedback from the secondary side, and some companies are prepared to pay that premium.BTW If it's got an integrated switch, it's called a converter, not a controller, so maybe you'll have more luck with that search term?

author: Warhawk
author_rank: Frequent Contributor
timestamp: January 30, 2016, 12:35:24 pm
content: Quote from: AcHmed99 on January 30, 2016, 12:57:27 amYou can have a look at my favorite - LM5001

author: DutchGert
author_rank: Frequent Contributor
timestamp: January 30, 2016, 01:29:27 pm
content: Best answer: because u are looking at the Military version of it. Always check the manufacturers site:http://www.linear.com/product/LT8302#orderinfoAvailable from$3.47 @ 1k.......On the other hand, :Linear in general is a bit (sometimes a lot) more expensive than others but the most sertainly offer u more.-Allmost nothing goes obsolete or has long leadtimes-Its all automotive specced so there QA standard is very high-Often there parts have nice nifty features that competitors don't-They have good specs-They are very robust.-Support is very goodupdate: you didnt try really hard to find a cheaper version right:http://canada.newark.com/webapp/wcs/stores/servlet/Search?pageSize=25&st=LT8302&catalogId=15003&categoryId=800000037007&langId=1&storeId=10196

author: DutchGert
author_rank: Frequent Contributor
timestamp: January 30, 2016, 01:50:11 pm
content: Quote from: AcHmed99 on January 30, 2016, 01:39:48 pmYes, if you buy 1 or 2 they indeed are. But like I said, Linear offers you a lot more then others in general. If you want to make a nice, simple, low part count, ~10W isolated supply I would quite like this one.But ofc you can allways go cheaper.
Why is voltage drooping so much when driving an RC servo (also ripple problem)? - Page 1
Forum section: electronics / projects

author: Involute
author_rank: Contributor
timestamp: May 18, 2016, 08:28:11 pm
content: I'm controlling an RC servo from a 5V Arduino (Pro Trinket). I'm supplying 5V to the entire system from a 5A bench supply. scope_0.jpg shows the supply output when the motor's idle. Scope_1.jpg shows the output when the motor is not quite stalled, at which point it's drawing about 800 mA. I have the current limited to 1.5A at the supply. Why is the voltage drooping so much, and why is the ripple so high? I would think a 5A supply should be able to handle this without breaking a sweat, but it's a Korad, not a Keysight, so maybe not.I tried a variety of caps across the supply output, but didn't see much effect until I got to 2200 uF (the biggest I have on hand). Scope_2.jpg shows the unloaded output, and scope_3.jpg shows it loaded. The ripple's a lot better in both, but the droop is still there under load.Explanations/suggestions greatly appreciated.

author: stmdude
author_rank: Frequent Contributor
timestamp: May 18, 2016, 08:32:54 pm
content: Wild guess: Tiny/thin wires involved. 0.8A*5V is quite a bit of power, meaning that the resistance in wires and traces become a big factor.

author: Involute
author_rank: Contributor
timestamp: May 18, 2016, 09:01:04 pm
content: Great idea! I'll beef up the related wires and report back. Thanks.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 18, 2016, 09:35:27 pm
content: add big capacitor near the servo

author: Involute
author_rank: Contributor
timestamp: May 19, 2016, 02:43:57 am
content: Upgraded the wire, no difference. Substituted a power supply harvested from somewhere that I had lying around and that solved the problem. Sounds like I need to ditch my Korad bench supply. Too bad. I really liked it until this.

author: kurt
author_rank: Contributor
timestamp: May 19, 2016, 05:59:13 pm
content: Quote from: Mechatrommer on May 18, 2016, 09:35:27 pmOr a "right size" capacitor near the servo.Looks like the current waveform have a very short rise time. So a big capacitor might have to much inductance to do anything about it. That might also be the reason the filter caps in the PSU can't deal with it.The servo can probably both have short rise times and relatively long pulse duration, so it could be that two caps are needed. A small low ESL to filter the sharp edges and a larger bulk capacitor to float it over the rest of the pulse. Then again, it could be that the PSU caps can handle the latter if the sharp edges are filtered enough by a small low ESL cap.

author: Involute
author_rank: Contributor
timestamp: May 19, 2016, 07:03:35 pm
content: How small and how low ESL?
Why is VSIM 0V? - Page 1
Forum section: electronics / projects

author: davegravy
author_rank: Regular Contributor
timestamp: April 11, 2024, 01:08:01 am
content: Before I repeat this madness for a 3rd time could someone please check my design (attached, see schematic page 2) for the SIM holder connection? Comments on other aspects also welcome.My design is a LTE-M cape for an SBC, it's based very closely on this sparkfun board:https://cdn.sparkfun.com/assets/d/7/b/c/3/lte_cat_m1_shield_schematic_v11.pdfI had JLCPCB make and assemble 5 of my boards minus the Ublox Sara-R5 LTE-M module because they're very expensive and I can't afford to buy 5 of them so I opted to buy just a couple and hand-solder the module.My first unit worked, powered up, AT commands over UART worked fine, but it wouldn't read the SIM card. I traced the issue to VSIM being 0V (if SIM is inserted or not). I double checked the schematic and layout and no obvious mistakes, so I figured it was a bad solder connection.All the module pads are buried so I'm working blind. I decided to try and reflow, but then it formed a short between the main supply and GND. So I decided to desolder, clean up the module and pcb pads, and try again. Turns out it's very hard to use tweezers to grab the module and NOT the shield while it's molten. The shield coming off wrecked the module.I soldered my second module on another board and same thing - everything worked except the SIM and again I measured 0V VSIM. This made me question that it could be a solder joint issue, what are the chances the same pad twice was the only one that failed to join?FWIW I checked impedance of VSIM to GND and it's >1MOhm. I also wrecked the 2nd module trying to desolder it, so now contemplating a third attempt as costs climbThis is the microSIM holder:https://www.lcsc.com/datasheet/lcsc_datasheet_2206302030_XUNPU-SMC-204-ARP6_C3446130.pdf

author: davegravy
author_rank: Regular Contributor
timestamp: April 11, 2024, 02:49:56 am
content: I'm thinking for a 3rd attempt rather than fully solder the module I'll just connect VCC, GND, PWR_ON and VSIM to the PCB via bodge wire and validate VSIM. Then only if that works I'll attempt another full surface mount solder

author: davegravy
author_rank: Regular Contributor
timestamp: April 12, 2024, 06:51:55 pm
content: I just discovered that the VSIM supply is a negotiated level using serial communication to the SIM card per ISO-IEC 7816-3.The SARA-R5 datasheet isn't clear how it handles cases of communication failure (e.g. due to connection issue or faulty SIM card). It may be disabling the supply to save power when it can't negotiate a supply voltage?I guess I'll have to probe to see what's going on with SIM_IO, SIM_CLK, and SIM_RST.

author: davegravy
author_rank: Regular Contributor
timestamp: April 13, 2024, 12:14:56 am
content: There seems to be an error in the Sparkfun circuit I copied. Theschematicshows aDT1042-04S0-7for the ESD diode array, however that model needs pin 2 and 5 tied to VCC not GND as is done in the sparkfun schematic.The actual manufactured product appears to use anESDA6V1BC6which will work with the GND connection.Sigh.
Why isn't there a USB-C 'hub'? - Page 1
Forum section: electronics / projects

author: Holes Flow
author_rank: Contributor
timestamp: July 18, 2018, 12:17:31 am
content: Experts,I know a guy who travels a lot for work, and he's asked if there is a way for him to reduce the charging/powering of all his USB-C stuff, which he is settling on as a standard for his gear. The standard I browsed over didn't seem to have any such limitation, so the only reason there aren't any out there must be something like current limitations, is my guess. Theymaysupply 1.5A or 3.0A at 5v in addition to baseline power provisioning. For USB 2.0/1.1 devices, 5V up to 500mA, and what they call USB Power Delivery can negotiate up to 20v at 5A...Could it be that there isn't a host controller that can do power negotiations on the dowstream legs, then take those values and do the power negotiation upstream?To be clear, I'm talking about a device whereby a single USB-C male plugs in to anupstreampower source, and 2 or moredownstreamUSB-C devices can be powered. I'm not concerned about a standard 'host controller' at this point, just trying to do power-unlessthe lack of a USB-C host controller to handle the downstream addressing is the barrier...So, why no hubs/switches?