hybridfree/eevblog-posts huggingface dataset:
Reverse power detection for Grid connected Inverter - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: December 06, 2018, 02:36:41 pm
content: I'm familiar with reverse power relays as used by utilities (ANSI 32) for detecting power direction, I'm not so sure what the renewable energy crowd is using to detect power direction (home-to-grid or grid-to-home)?Are there any OTS affordable reverse power detectors available for this market?

author: DaJMasta
author_rank: Super Contributor
timestamp: December 06, 2018, 07:34:59 pm
content: Would a current clamp be sufficient? It will give you direction of current flow, and while I don't know of commercial products that just detect and report it for for this kind of application, it seems simple enough that they probably do exist.

author: jbb
author_rank: Super Contributor
timestamp: December 06, 2018, 08:09:22 pm
content: A current clamp is only part of the solution. Because AC power is ... AC you’ll see positive and negative currents in any case.To measure power flow direction you need voltage and current measurements (like a power meter).Not sure of any domestic / commercial stuff to do this. Industrial protection relays or transducers as probably available for purcha$$$e.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: December 07, 2018, 03:01:53 am
content: Quote from: Jester on December 06, 2018, 02:36:41 pmWhat you need is a power meter. It measures current and voltage and the phase between them. That determines the direction of current flow.https://www.powermeterstore.com/category/residential-power-energy-meters
Reverse sawtooth synthesizer vco now oscillates at low frequencies.  - Page 1
Forum section: electronics / projects

author: Ryan OMalley
author_rank: Newbie
timestamp: March 15, 2020, 09:44:51 pm
content: Hi everyone, about a month ago I posted that my reverse-sawtooth vco wouldn't run below 96 hz. the fix was to add some hysteresis to the comparator by adding a 10k resistor between the non-inverting and inverting pins, and placing a 0.1uf capacitor across the jfet. the circuit now can oscillate between 16hz to 2900hz, which is a good range for the purpose i'm going to be using it for, an analog polyphonic synthesizer. The only problem that i'm having with it at the moment is that the voltage-controlled current sink is not responding fast enough to control voltage changes. I have tried adding resistors and capacitors in the negative feedback loop, but the circuit still doesn't respond fast enough. I will attach the Revision 2 schematic (in pdf form) below. any suggestions on how to improve the responsiveness of the voltage controlled current sink would be greatly appreciated.

author: Zero999
author_rank: Super Contributor
timestamp: March 15, 2020, 10:45:04 pm
content: You might get more help if you kept everything related to your project to one, single thread.

author: duak
author_rank: Super Contributor
timestamp: March 16, 2020, 04:40:11 pm
content: R O',What are C? and R? for? If the left side of C? is grounded or connected to a low impedance source, it will add a time delay to the frequency control input. I would connect the right end of R? to the -input (pin 2) of U1A.Will the left end of R7 ever go open circuit?Why is C2 across J113 and not C1? It is conducting any noise on the +12V into a critical node of the oscillator. I also question the value of C2. I seems very large for the frequency range you are after.R4 has a value of 3M0. I think this affect the upper frequency limit and would reduce the value to, say 47K.I can't see how R12 materially affects the hysteresis of the comparator. I would move it to connect U2B-7 to U3-3 and add a large resistor (3M0 or greater) between U3-3 and U3-1. This gives some positive feedback. If this affects the upper frequency limit, try reducing the relocated R12. Note that this change requires a lower value for R4.BTW, are all the VEE or - power pins of U1 & U2 connected to -12V?
Reverse Sawtooth synthesizer vco- seeking feedback to improve design - Page 1
Forum section: electronics / projects

author: Ryan OMalley
author_rank: Newbie
timestamp: February 09, 2020, 09:38:48 pm
content: Hi everyone, I'm working on a reverse sawtooth VCO that is controlled by a linear control voltage. my design is inspired from VCO designs that various analog Yamaha synthesizers used in the 1970's. I went with the linear volts/hz control method so that I wouldn't need to have an exponential converter circuit, and so that I can run control voltage into it right from a DAC circuit It works fairly well, except that the circuit won't oscillate below 96 hz. I'm not sure if I need to increase the capacitance or add hysteresis to the comparator. I will attach the schematic diagram and a picture of the output waveform on my oscilloscope. any suggestions on how to improve this circuit would be greatly appreciated.
Reversed biased diode for beeper... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: July 06, 2015, 02:51:54 pm
content: I'm using a PZT2222 to drive a "5V active beeper" that I bought off eBay. I recall using these in the past and didn't notice much of a kick back when turning one off, but I just took a look at it with my scope and it shows a 200ns pulse of 63V. The PZT2222 data sheet says the CE voltage max is 40V. Does this mean I need to use a reversed biased diode? Is 200ns short enough that it isn't necessary?

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2015, 03:06:03 pm
content: I haven't heard the concept of a pulse being too short to be damaging... it might slow down the damage perhaps, but I'd be putting the diode there if I were you. Maybe I'm overly conservative though.
Reversed PFET between USB and 5V rail - How does it work?  - Page 1
Forum section: electronics / projects

author: Starlord
author_rank: Frequent Contributor
timestamp: March 20, 2015, 04:41:12 am
content: So I've got this in a circuit I'm making some modifications to. It resembles a method of reverse polarity protection I'm familiar with, but I'm having a hell of a time wrapping my head around what's going on inside the PFET.I would assume this disconnects the 5V rail from the USB when 5V is present. But that doesn't make sense.First, because why disconnect the 5V from the USB if 5V is present on the rail, unless perhaps it might be slightly lower than 5V and cause power to flow back into the PC?And second, because if 5V is present on the USB, wouldn't it make the PFET turn off as soon as it turns on, since the source and gate would be approximately equal instead of the source being much less than the gate?Maybe that's how this works? The PEFT just goes into a state where it balances between on and off? But wouldn't that put it in a high resistance state?What's going on here?

author: Kjelt
author_rank: Super Contributor
timestamp: March 20, 2015, 10:55:52 am
content: If +5V is not present the USB 5V will pass through the freewheelingdiode/bodydiode of the fet and power the +5V.When the 74LVC1G output is 1V less than +5V so less than 4V the FET will conduct to its Rds on of 70mOhms. So what is the input of the 74LVC1G ?Probably it is a protection for the USB port, so when +5V is present but USB is 0V it will not set the FET to conduct and the diode blocks the +5 going into the USB something like that.If the USB is an output only than it makes sense the fet just blocks the 5V to the USB till the output of the gate is set low. So it is simply a USB powerswitch in that case.

author: Starlord
author_rank: Frequent Contributor
timestamp: March 20, 2015, 12:18:30 pm
content: I think I understand maybe.That input to the 74LC is USB_HOST_ENABLESo I think what's going on here is:1. When 5V is coming in through the USB, it can pass through the PFET body diode regardless of whether it's on or off.2. When the device is a host, the PFET gate is pulled down, turning it on. This opens the path for the 5V rail to be connected to the USB to power external devices.3. When the device is a slave, the PFET gate is pulled up, turning it off. As stated above, even when he FET is off, it still conducts through the diode, so the USB can supply 5V to the system, if available.4. And I guess the resistor there pulls the gate up to turn the FET off until such time as the microcontroller is able to assert the host pin high or low to set the PFET into a known state.

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: March 20, 2015, 07:57:45 pm
content: http://provideyourown.com/2012/reverse-polarity-protection-circuits/!
Reversing Acura/Honda CD changer protocol - Page 1
Forum section: electronics / projects

author: twizzter
author_rank: Contributor
timestamp: January 17, 2021, 09:39:16 pm
content: Some time ago i came up with idea - to link phone with OEM radio unit using CD-changer extension connector.Did some cable-digging and measurements. It appears that changer talks with head unit using IEBus protocol.I designed HW interface and wrote small program to sniff data between radio and changer.Currently i'm able to catch frame and display its contents, for example:Code:================================================Frame 9 detected: (monitor mode)Type RegularMaster addr 0x100Slave addr 0x136 (ACK)Control bits 0xf (Write data) (ACK)Payload len (B) 7 (ACK)Payload 0x40 (ACK)Payload 0x0 (ACK)Payload 0x36 (ACK)Payload 0x2 (ACK)Payload 0x7 (ACK)Payload 0x3 (ACK)Payload 0x9b (ACK)================================================Altough i've managed to guess some basic stuff, like device addresses and current track number, most of payload data is still unclear to me.I believe audio is made by Pioneer - company was using IP-BUS in some devices, but i couldn't find any technical details.Does anyone have experience with this type of protocol?
Review and Feedback Request: Battery Management Circuit with AXP209 - Page 1
Forum section: electronics / projects

author: amanj1
author_rank: Newbie
timestamp: December 27, 2024, 06:41:43 pm
content: Hello EEVblog community,I hope this message finds you all well. I am currently working on a project involving a multi-effects device, and I’ve designed a power supply and battery management circuit using the AXP209 power management IC. I would be deeply grateful if you could take a look at my schematic and provide your valuable feedback regarding its correctness and potential areas for improvement.Project Details:Primary Goals:Power the system from USB when connected.Manage and charge a 3.7V Li-ion battery when USB is available.Ensure proper battery monitoring and safe charging.Key Components Used:AXP209: As the primary PMIC.Sufficient decoupling capacitors for VBUS, ACIN, and other critical points.A 0.02Ω resistor for battery current sensing.Specific Questions/Concerns:Are there any potential issues with the connection of BAT and BAT_SENSE, particularly the placement of the current sense resistor (R5)?Does the decoupling around ACIN, VBUS, and VIN look adequate?Are the configurations for the LDO outputs (e.g., LDO1, LDO3) and the associated capacitors appropriate for stable operation?Are there any additional considerations for thermal management, ground plane design, or signal integrity (e.g., I2C lines to the microcontroller)?Additional Note:I’m a beginner in electronics, so I sincerely hope your guidance can help me learn and develop a deeper passion for this field. Your support will mean a lot to me and will surely inspire me to dive deeper into the world of electronics.Attached Files:I have attached the schematic for your review. Please let me know if additional details or design files are needed.Your feedback will be invaluable in ensuring the reliability and performance of this design. Thank you in advance for your time and assistance!Kind regards,Electronics Enthusiast
Review Layout with INA253 (current sensing) - Page 1
Forum section: electronics / projects

author: waulu13
author_rank: Newbie
timestamp: October 23, 2020, 09:08:49 am
content: Hello,I made a simple layout with three INA253 (U1, U2, U3) in parallel. In the beginning I will only solder one. Eventually I will add the second and the third if everything goes well. The datasheet of INA253,https://www.ti.com/lit/ds/symlink/ina253.pdf?ts=1603359713113&ref_url=https%253A%252F%252Fwww.google.com%252FI will manufacture the PCB with 1oz and after that I will add solder over the tracks with high current. The conenctors I will use something like this,https://pt.mouser.com/ProductDetail/TE-Connectivity/796949-3?qs=ItShc8fFPOsPQ5f70MLFFw%3D%3DSo with only one INA253 (10 A), are the layout and the connectors acceptable? Once I add the 2nd and the 3rd INA253 I will keep the tests with 15A maximum just to measure the results and test software. The decoupling capacitors C1, C2 and C3 are well positioned too?Best regards,EDIT: The ground is still not connected to the connector.
Review my power circuit - Page 1
Forum section: electronics / projects

author: DTJ
author_rank: Super Contributor
timestamp: June 09, 2015, 01:10:37 pm
content: I want to run a little micro circuit off a battery and have it turned on and off via a normally open push button switch. What do you think of the attached circuit?The button is pressed momentarily to turn the circuit on. To turn it off the button is pressed and held for a couple of seconds.I mucked up the text on the schematic "S" is the "Sel" switch.Data sheet for the LP2951 voltage regulator:http://www.ti.com/lit/ds/symlink/lp2950-n.pdfSee any gotchas before I try it out?

author: flynwill
author_rank: Regular Contributor
timestamp: June 09, 2015, 01:49:14 pm
content: The biggest flaw I see is if the user isn't patient enough to hold down the switch until the micro gets booted far enough to raise the "PWR_ON" signal. I would add hardware flip-flop to latch the power state on immediately.On many micros the I/O pins default to type Input until programmed otherwise. If that is the case here then the fix is as simple as a pullup resistor from the PWR_ON signal to the output of the regulator. Then once turned on the power stays on until the processor actively enables the output and pulls it low.You also might want to add an override of some sort so that you have a way to shut it down if it crashes (and is no longer paying any attention to the "SEL" line), unless it's easy enough to just pull the power cord in that event.

author: Pillager
author_rank: Unknown
timestamp: June 09, 2015, 02:03:12 pm
content: Just to give you an alternative:Dave's video on the subject.And the forum thread:https://www.eevblog.com/forum/blog/eevblog-262-world%27s-simplest-soft-latching-power-switch-circuit/msg170405/#msg170405

author: DTJ
author_rank: Super Contributor
timestamp: June 10, 2015, 03:24:18 am
content: Hi Flyn,This is going to be used in a bit of test gear so I wanted to ensure the user holds the button for a second or so before it powers up to avoid "bumping" of the power switch causing it to turn on.Using a pullup on the default input state pin is an interesting idea. I might play with that.Tom, I saw that video of Dave - it actually gave me the inspiration to get of my backside and work on a soft switch for this project.Thanks for the feedback gents.
Review of a beginner's HV design - Page 1
Forum section: electronics / projects

author: kesterlester
author_rank: Newbie
timestamp: May 05, 2020, 01:46:52 am
content: Attached is a picture of an early draft of a relay board I am designing just for non-commercial use in our home, to work around limitations in an existing central heating controller.The (hard to see) grid overlaid on the image has 5mm squares.I am mainly interested to see if any other users have comments about potential mains-isolation / safety issues in my design, as I am not experienced in designing for mains voltages.The board itself will live inside a box with no user interface or buttons (just a closed box with air-vents, etc) as it will be controlled from outside wirelessly. My main concerns are just the passive safety of the board wrt itself (i.e. that it shouldn't set itself alight, etc, and that if it fails it does so gracefully) through reasonable compliance with sensible guidelines.The board has a HV side 80% of which is just relays to turn on and off 240VAC based central heating zoning valves, etc. The remaining bits are a fuse and an (optional) off-the-shelf encapsulated PS that might be used to power the LV side of the board if that side doesn't get battery powered.The main place where I have my doubts as to regulatory compliance concerns the pads under the POWER-IN connector near the 3A fuse. It has 2mm-wide pads with a 5mm pitch which puts 3mm creepage between the live pads. Nearly every ebay-sold optocoupler relay board has these connectors for the mains side of the relays, so I imagine they are pretty safe in practice, however that does not necessarily mean they meet regulations. I am not too worried about the space between the pads on the other connectors as they come AFTER the fuse, where I believe 3mm is OK?However, is the Live-Earth separation OK between the two pads at the extreme bottom left?[ Aside 1: Although I have put a 3A fuse on the board, I should note that the power that supplies it will have come from a permanent wiring to the existing CH controller which has it's own 3A fuse. So perhaps the "pre fuse" part of my board counts as "post fuse" ? ][ Aside 2: The cyan thing above the fuse is a slot cut to increase the creepage between its pad and the LV side of the board. The board will be coated (except on its pads, of course) with insulating solder-resist, and the components are all encapsulated except on their legs, so I think the problem is confined to assessing pad safety, and board to enclosure safety -- not worries about track-to-track safety on the HV side. But again, please comment if you think there are big problems I've not spotted. ]
Review of Master–Slave T‑Flip‑Flop State Table - Page 1
Forum section: electronics / projects

author: AlexP90
author_rank: Newbie
timestamp: July 19, 2025, 08:34:34 pm
content: Hi everyone,I’m designing a rising‑edge master–slave T flip‑flop (master latch enabled at a=1, slave latch enabled at a=0) and have derived the full 3‑bit state‑transition table q_{xyz}, wherex = slave’s Qy = master’s Qz = data loaded into the master (i.e. T XOR x)I attached a screenshot of the table, where (columns = (a,T), rows = current q_{xyz}, entries = next state q_{x′y′z′}, “–” = unreachable):So I wanted to know if the table I wrote for the T master–slave flip‑flop is correct. To write the q_i in the cells I used that rule: when a=0 → x′=y, y′=y, z′=D; when a=1 → x′=x, y′=z XOR x, z′=z. But I’m not sure this is correct.Questions:1. Are all my next‑state entries correct?2. Are the don’t‑care placements (“--”) valid?Thanks in advance for your feedback!
Review on YiHua 878D - Page 1
Forum section: electronics / projects

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: May 09, 2019, 04:38:35 pm
content: Hi,I am planning to buy YiHua 878D 2 in 1 soldering rework station. Previously, I have used Hakko's FX-888D soldeing station and YiHua 858D rework station. This time I want to take an integrated one(multi-function) like 878D. Please let me get your review/comments on this product. Will it perform at-least parallel(or comparable) to the FX-888D & 858D?TIA.Regards,

author: OM222O
author_rank: Frequent Contributor
timestamp: May 09, 2019, 04:46:26 pm
content: I bought the 862D+ off of amazon. it's been pretty decent so far, but the supplied conical tip with the iron is garbage and dies quickly. I also had the magnetic switch in the hot air gun break but after replacing it with a high quality one everything has been buttery smooth. the main advantage is it's so cheap, you can't beat it in terms of value.

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: May 10, 2019, 04:57:03 am
content: Any suggestions/comments on YiHua 878D..?Regards,

author: OM222O
author_rank: Frequent Contributor
timestamp: May 10, 2019, 05:24:57 am
content: all yihua products are basically the same, with some marginal differences in the feature set which you can find on their website. what I said about the 862D+ holds true for the 878D as well. just check the feature set before you buy (862D+ is a better version and not that much more expensive than the 878D).
Review Request For ESP32 Board - Page 1
Forum section: electronics / projects

author: RaptorHunter
author_rank: Newbie
timestamp: September 09, 2021, 08:55:55 am
content: Hi everyone, I put this together, can you check if everything it's OK?It's a board to drive 2 4W 3535 RGBW LED ceiling starlight wired in series, a 28BYJ-48 that makes the star twinkle effect, and LED strips around the ceiling.https://oshwlab.com/farukcorreia/esp32-led-stepper

author: PeteH
author_rank: Unknown
timestamp: September 09, 2021, 12:15:58 pm
content: Esp32 is a 3.3V logic device (I/Os are not 5V compatible)

author: t1d
author_rank: Super Contributor
timestamp: September 10, 2021, 01:30:57 am
content: Interesting project. Keep going and keep us posted.

author: bson
author_rank: Unknown
timestamp: September 11, 2021, 07:55:38 pm
content: You probably can't have 5V on the GPIO pins. It will leak in through the TVS diodes on the IO pins and onto the supply rail, and lift it to 5V while the ESP32 is in reset during power-on - or whenever else it draws less than 0.2mA or so. This will either immediately or eventually destroy 3.3V CMOS.

author: floobydust
author_rank: Super Contributor
timestamp: September 11, 2021, 09:05:48 pm
content: U1 ULN2003 pin 9 COM should connect to +12V, not +5V if the stepper motors are 12V powered. It's also 5V input and for 3.3V the ULN2003 would not be getting much drive. Maybe look at ULN2001 plus base resistors.
Review Request - HDMI TX, concerned about the crosstalk - Page 1
Forum section: electronics / projects

author: HasanSyr
author_rank: Contributor
timestamp: August 02, 2025, 05:41:27 pm
content: Hello, this is a custom FPGA Dev Board built around a SOM. Im concerned about crosstalk between the Video In signals at the bottom and the Video IN CLK since its also close to the 165 MHz digital signals.Im most concerned about the SOM traces being differential pairs.There are 2 HDMI outputs. The number of pins barely fits in 1 bank.To avoid crosstalk on the SOM, I can route each signal only on the P traces (for example) and move HDMI2 (for example) to another bank. Presuming each pair on the SOM has adequate spacing this would solve my issue at the cost of now having many N single-ended traces scattered around, making them far away from the expansion/IO connector (expansion is just left over pins). This would also mean I have less expansion/GPIO diff pairs.So I'm wondering if the crosstalk will be low enough so I wouldn't have to do this.
reviewing my board design - Page 1
Forum section: electronics / projects

author: oriagranat9
author_rank: Newbie
timestamp: March 06, 2020, 06:25:55 pm
content: hey im making my first board using the raspberry pi compute module 3+ and was wandering is someone can review my work and tell me if its correct and will work plus give me some advice to improve it.the board is powered from a 12v battery and is used for vision detection using the camera port.thanks in advance.(schematic as pdf)

author: thm_w
author_rank: Super Contributor
timestamp: March 07, 2020, 01:13:47 am
content: Looks good, you've just posted the schematic, no board.You are missing a connection on D2 cathode to the inductor (no dot).You may consider adding a few spare IO test points, in case you need IO, but if you're sure its for camera only then it might be fine.

author: VanBudd
author_rank: Contributor
timestamp: April 23, 2020, 11:40:34 am
content: You should place a 10k pullup resistor to 3V3 on the ENC28J60 Chipselect pin, i had problems without pullup.The RBIAS pin should be conntected with a 2.32k to GND.VCAP capacitor should be 10uF.In the ENC Datasheet is a example schematic.For 3V3 and 1V8 i used PAM2306 from the original PI, it works just fine.Maybe a 220ohm ferrite between 3V3 and Ethernet 3V3.Dont know your ethernet wiring, but if its a standard wiring it should be working.For ethernet i use this schematichttps://www.acmesystems.it/www/CM3-HOME_schematic/cm3home_schematic.pdfHope that will help you a little bit
Revising a nixie tube clock project - Page 1
Forum section: electronics / projects

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: May 20, 2013, 06:31:46 am
content: Hello i have recently been revising my first schematic for my nixie tube clock project to get rid of alot of silly problems such as the cr1220 holder was connected the wrong way so the battery had to be put in upside down ect. Picture of the rev 1 nixie tube clock :I have finished revising it and have made many changes such as the battery holder and replacing the old 74141 nixie driver to a cmos 4028 with high voltage npn transistors as the 74141 was very prone to ESD.The circuit is based off of an arduino and i am now wanting to put a smt arduino onto the board (along with making everything else smt so i can fit a battery or two into the clock to make it portable.In the top left of the schematic for rev 2.0.1 i have put a string of diodes in to drop the voltage before going i to the voltage regulator because due to the size of the case i am unable to fit a big enough heatsink into it (see the rev 1 photo)This is my revised schematic 2.0.1 as i noticed a few problems In Rev 2 myself.It would be very helpful if people could see any problems and let me know as i dont want to go to another revision after i have made this project again.
Revisiting a panel meter problem. - Page 1
Forum section: electronics / projects

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 15, 2023, 01:01:27 pm
content: Some time ago I put together a power supply (linear) and used one of these cheap digital panel Volts Amps meter. This PSU was intended to power a HF linear amplifier. Running it works fine on most loads resistive and inductive, but when it powers the HF linear amplifier the meter display goes iratic and shows values all over the place when the radio and amplifier are keyed up. I gave up on this power supply for a long time, but recently wanted to see if I can resolve the issue. Originally the meter is being powered from itself, so no extra PSU to power the meter. So my question is, can it be possible that the load amplifier, while it pulls the correct about of voltage and current, could the slight voltage drop under load send the volt amp meter into this unreadable state ? Or would an independent power source for the meter resolve the problem, such as an additional plug in power adapter. So completely independent power source for the meter. Or is it more likely to be stray RF energy sending the meter into an unreadable state. I will try an independent power supply to power the meter just to see what happens. But thoughts appreciated. Below is the two meter wiring configurations. The meter in the PSU is wired up from its own supply, so self contained at the moment.

author: xrunner
author_rank: Super Contributor
timestamp: October 15, 2023, 01:09:20 pm
content: I bet it's RF coupling making the display erratic, since it happens when you use the linear amp. Might need separate PS, ferrites, or sheilding for the display.

author: davelectronic
author_rank: Frequent Contributor
timestamp: October 15, 2023, 06:56:04 pm
content: Thanks for your reply, yes shielding might work if an independent power source fails. I could solder together a small copper box, and try that. But it still leaves the display open, except for the diffuser plastic panel. Shame really, the meter works fine with all other loads.

author: p.larner
author_rank: Frequent Contributor
timestamp: October 18, 2023, 02:32:14 am
content: bet its rf,try 0.1uf decoupling caps from all wires to a good ground.
Revisiting design of "safely" metering AC power, please critique! - Page 1
Forum section: electronics / projects

author: bsodmike
author_rank: Regular Contributor
timestamp: July 22, 2021, 06:31:03 am
content: Hi all,Previously, many here have recommended all-in-one ICs that can do this job, but given the latest chip shortages, I've been looking at various approaches taken by others. One in particular is the Open Energy monitor approach for measuring AC voltage using circuit (see attached Arduino-AC-voltage-input-1.png).https://www.youtube.com/watch?v=PSzkaSy5lHY&ab_channel=GreatScott%21However, in the above youtube video one person commented:QuoteAnd they provided a simple example, attached (screenshot) with OpAmps to "clamp" the voltage provided to the microcontroller. Thoughts?Are there any better approaches to maintaining isolation between the microcontroller and the AC supply?Thanks!

author: David Hess
author_rank: Super Contributor
timestamp: July 22, 2021, 06:49:11 pm
content: The impedance after the divider is about 10 kilohms so any current beyond the power rails is limited to 500 microamps which is not going to damage anything. Still, I would include external clamping with diodes or transistors and some RC filtering to remove high frequency noise and spikes.
Revisiting my pulse generator - Page 1
Forum section: electronics / projects

author: c4757p
author_rank: Super Contributor
timestamp: August 29, 2013, 08:05:09 pm
content: A few months ago, I made apost hereabout a building pulse generator - specifically the output section, which was supposed to develop a variable-amplitude, "fast" (<5ns rise/fall) signal from a digital input.That project has been on the shelf for a while, and I've decided I'd like to try to redesign this part of it, because there are a few things I don't like about it. (1. Semi-obsolete parts - 2N2369 - yes, I know there is MMBT2369. 2. Not the cleanest waveform. 3. Huge di/dt means it has the potential to radiate EMI like a lightning storm. 4. "Variable" output voltage depends on VCC, meaning a fairly beefy variable power supply.)Here is my current redesign of the signal generation piece. This generates a lower-amplitude (about 2V maximum) signal, which will be amplified and driven to the output in a separate section. (This is why the output is into 100 ohms, not 50: 100 ohm microstrip trace.)The disconnected R4 represents the variable attenuator, which will be a small bank of resistors and switches to form a digitally variable voltage divider. The disconnected C3 represents the variable rise/fall time limiter, which will work the same way, except using capacitors.The input is a fast rise time signal at fixed amplitude, most likely from a 74AHC inverter (or another "fast" logic family with a fair amount of drive capacity).The inductors L1 and L2 give a somewhat cleaner signal. I'm a bit embarrassed to say I don't fully know what's going on, but I tried it and it worked...My guess is by reducing the apparent capacitance to the supply rail through the B-C junction.The little circuit around Q3 is just a level shifter. The multiple stages of buffers prevent too much loading (especially capacitive) of the attenuator.I'd include the SPICE file, but I'd have to pack up the BFS17W model, and I've got to run to class now. Sorry!Any comments, criticisms, suggestions or insults?

author: c4757p
author_rank: Super Contributor
timestamp: August 29, 2013, 08:19:25 pm
content: Whoops - the trace shown is the output, between the two 100 ohm resistor.Second question: for the attenuator switches, I need NPN transistors with relatively low collector capacitance when switched off. In the simulation, BC8xx (the full number eludes me) was OK, but I'd still prefer better. Off-state collector capacitance isn't a searchable parameter on any of the big web sites. Does anyone know of a good transistor for this?
Revox B261 audio relay PCB's for sale-How to do it properly? - Page 1
Forum section: electronics / projects

author: djsb
author_rank: Super Contributor
timestamp: October 15, 2023, 02:46:12 pm
content: I have a few spare PCB's for sale for a small Revox B261 tuner project. I made a small PCB that replaces the original single relay (which had faulty, corroded contacts) on the audio board. The single relay was replaced by two AXICOM IM07 relays. I have a few of the PCB's spare that I could sell, but I'm not sure how to go about it. Not even sure if anyone would want to buy one. Should I offer the PCB files as a paid option or a free download from somewhere? How do I make sure I'm not liable for any damage that may result from improper installation of the PCB (some kind of liability statement). The board works fine as I'm listening to the tuner now that has the board installed. Where would the best place to sell this small number of boards (I have about 5 or so left). Any advice welcome. Thanks.

author: jonpaul
author_rank: Super Contributor
timestamp: October 16, 2023, 06:18:06 am
content: What problem does this solve?Suggest you donate to Swiss museum enter.ch, they have a lot of old Revox equipment and techs that restore.Jon

author: djsb
author_rank: Super Contributor
timestamp: October 16, 2023, 06:37:20 pm
content: Quote from: djsb on October 15, 2023, 02:46:12 pm
REW scope visual artifact - how to avoid? - Page 1
Forum section: electronics / projects

author: dobsonr741
author_rank: Frequent Contributor
timestamp: May 02, 2023, 12:51:18 am
content: I'm new to REW, and I like the scope function of it. However, it seems to me the sampling frames are stitched together artificially and creating jumps not present on my otherwise perfect signal. Is there a setting to avoid the stitching?BTW, this is REW:https://www.roomeqwizard.com/help/help_en-GB/html/scope.html#top
Rewinding a toroidal transformer...what voltages would be good? - Page 1
Forum section: electronics / projects

author: xenoxaos
author_rank: Contributor
timestamp: August 02, 2021, 09:08:02 pm
content: I've got a 115v to 27v transformer. I was wanting to rewind it so I'd at least have a center tap for +/-12v. It seems to be fairly beefy for my needs so I was wanting to rewind it for multiple uses. What output voltages would all of y'all recommend winding.Should I go with center tap or just two windings I can separate/combine at will.

author: Gyro
author_rank: Super Contributor
timestamp: August 02, 2021, 09:24:11 pm
content: Two windings halve the length of wire that you have to wind on at one time.

author: james_s
author_rank: Super Contributor
timestamp: August 02, 2021, 09:58:54 pm
content: When I've wound transformers like that, I wound a single bifilar winding to get two separate identical secondary windings I connected in series as a single center tapped winding. Half the amount of work as two separate windings and a lot easier to make sure it's identical which is important if you ever want to wire them in parallel.

author: pqass
author_rank: Super Contributor
timestamp: August 02, 2021, 10:16:33 pm
content: Temporarily wrap 10 turns of insulated wire around the toroid, apply mains to the primary winding, and measure the 10 turn winding (leaving the existing 27V winding unconnected). Divide by 10 to get a volts/turn value.Now you can use the volts/turn to dial any voltage you may need.If there is enough room, you don't even have to unwind the 27V winding; just leave it unconnected.Do you know the power rating (in VA) of the transformer?If so, just make sure that any/all new secondary (or secondaries combined) don't exceed the VA (ie. the wire diameter chosen amp carrying capability multiplied by the voltage).If not, use the diameter of the existing 27V wire as a rough approximation of the current capability (lookup dia->amp in table and multiply by 27V to get VA).If your new secondary is wound to produce less voltage, you can increase its diameter proportionally to give more current.
RF Amplifier Impedance Matching? - Page 1
Forum section: electronics / projects

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: March 06, 2025, 06:20:53 am
content: Hey all,I am messing around with a rather low power RF amplifier design that will operate on the 20m band. I am mainly doing it as a proof of concept to gather more knowledge rather than actually building something to use. I have gotten a circuit designed and built for the most part, all I am missing now is my input and output transformers.My current topology is a Class AB push pull amplifier using 2 FDP3682 MOSFETs (not the best choice but they are what I had) and using a input transformer for both impedance matching and converting the signal from unbalanced to balanced for the gates. My idea was to just wind a 1:1 transformer and connect a VNA to measure the input impedance. While I am getting results that make sense, I was curious what others might recommend?Also, say I get a hypothetical measurement of 30 + j120 for my impedance, is there a recommended method to started transforming this to 50 ohms? I have seen others take |Z| and use the ratio of that and 50 to get their turns ratio and then tune that but are there better ways of approaching this?Thanks!

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 06, 2025, 12:37:19 pm
content: Depends on what your goal is....If you want to maximize small signal gain, then you want to conjugate match the input impedance to your source (using whatever combination of L/C/transformer/etc you like).But for a power amplifier I wouldnotrecommend going for maximum gain. It tends to lead to issues with linearity, bandwidth, and stability down the road.It's common to modify the circuitry around the amplifier itself to lower its gain while making it more broadband and linear (for example, gate shunt resistance, miller feedback resistance, source resistance, etc). These also lower the gain, but so long as you still have 15-20dB that should be fine. At the same time, these modifications can also allow you to freely change the input impedance of the amplifier, making impedance matching much easier.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: March 08, 2025, 04:05:23 pm
content: Mix 43 ferrite works okay for lower HF bands but may have higher losses at 14 MHz. Mix 61 is a better choice for lower loss at this frequency.

author: TimFox
author_rank: Super Contributor
timestamp: March 08, 2025, 04:41:17 pm
content: For a small-signal amplifier, conjugate matching gives maximum power gain.For a large-signal power amplifier, with its specific power supply, the optimal load impedance seen by the active circuit for maximum available power is not, in general, a conjugate match to the output impedance of the amplifier.
RF Amplifier Layout-Confusion Analog Devices - Page 1
Forum section: electronics / projects

author: Arsh ahmad
author_rank: Regular Contributor
timestamp: February 07, 2025, 08:55:00 am
content: Hi,Currently I am testing ADL5523 RF LNA from Analog Devices through its official Eval Board, now I want to design a custom board for the same. I checked the eval board design, there is a PCB trace based Variable resistor but there are few NPTH holes at top and bottom of the IC, I want to understand the purpose of those and is it necessary to remove the mask from the vias.Thanks in advance

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: February 07, 2025, 06:05:51 pm
content: I think these holes are for heat dissipation. The ADL5523 LNA dissipates power as heat. Good thermal dissipation is a must for stable performance. If the PCB is mounted to a heatsink, these holes can help improve thermal conductivity
RF Combiner Port Isolation - Page 1
Forum section: electronics / projects

author: WBB
author_rank: Regular Contributor
timestamp: December 18, 2015, 09:54:18 pm
content: I'm sure this is a dumb question bit I'm gonna raise my hand and ask anyway!If someone were to transmit two signals into a combiner at well above the port to port isolation values what sort of horrific things would appear at the output? Noise? Distortion? Santa?If it matters, the signals in question are 256 qam.Thanks!

author: rfeecs
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:23:50 pm
content: The question doesn't quite make sense.Isolation is a ratio (like 20dB isolation).The power you put into a port is an absolute value (like 25dBm).So in that case, if each transmitter was putting 25dBm into each port, 5dBm would leak through from the output of each transmitter to the output of the other.The most likely result would be some mixing between the two signals, resulting in intermodulation distortion. The unwanted signal could effectively overdrive the transmitter, for your qam signal giving you AM or PM distortion.

author: KJDS
author_rank: Super Contributor
timestamp: December 18, 2015, 11:29:22 pm
content: In practice, most commercial transmitters have isolators on their outputs protecting them from incoming signals, and every cellphone basestation transmit combiner I've ever seen has an isolator on each input. Without these, then some unwanted signal would be entering another transmitter and would cause distortion, the exact nature of which would need a careful study of the transmitter to determine.

author: WBB
author_rank: Regular Contributor
timestamp: December 19, 2015, 10:55:13 am
content: Thanks for the info. Sorry the question wasn't quite clear. I've tested this a little bit myself but I lack the knowledge and equipment to really know what is going on. What I have tried is combing a few signals (20db port isolation) with levels ranging from 15dbmv up to 60dbmv and I can see no difference in mer, ber or constellations. To be clear, the levels at the combiner inputs were the same for each input, I just varied the level of all signals to see what would happen. I can see where there could be problems if one input was 15dbmv and the other was 60dbmv but my question is assuming each input is at the same level.Thanks again!

author: KJDS
author_rank: Super Contributor
timestamp: December 19, 2015, 12:52:22 pm
content: The answer lies entirely within what you are using to generate the signals.

author: WBB
author_rank: Regular Contributor
timestamp: December 19, 2015, 04:09:21 pm
content: Yes, thanks. It finally dawned on me. I knew it was a dumb question, I just didn't realize how dumb!
RF device, 2 or 4 layer? - Page 1
Forum section: electronics / projects

author: TommyGunn
author_rank: Contributor
timestamp: July 28, 2012, 06:48:55 pm
content: Hey allI am working of the design of a low power wireless device and am wondering what affect is on the signal stability when I change between a 2 or 4 layer design.I am using the 2.4Ghz Ant technology. We have to use a chip antenna due to size constraints.Thanks!

author: RidiculousRichard
author_rank: Newbie
timestamp: July 28, 2012, 10:20:02 pm
content: Hi,The sole time I saw someone else with both 2 layer and 4 layer versions of a high speed design there was a huge difference in size to get similar signal integrity. With the 2 layer board, the ground plane is so much further away that your high speed traces are much larger to get the correct impedance (without checking ~50mils rather than ~6 mils) and you need to space out the traces in proportion to avoid cross-coupling. The guy seemed to cope with the greater impedance mis-match at components but the 2 layer was definately worse than the 4 layer.Some advice from others can be found here:https://www.eevblog.com/forum/beginners/simulation-software-for-people-moving-into-high-speed-%28gt200mhz%29-pcb-traces/All the best,Richard

author: nctnico
author_rank: Super Contributor
timestamp: July 28, 2012, 11:07:25 pm
content: What you want is 2 layers close to each other so you can use narrow striplines. Most PCB house have the possibility to order PCBs with a thinner epoxy carrier. If this doesn't cause mechanical problems it is a solution to use a 2 layer board. Otherwise you are stuck with a 4 layer board.
Solved, obsolete. - Page 1
Forum section: electronics / projects

author: evb149
author_rank: Regular Contributor
timestamp: October 04, 2015, 06:39:19 pm
content: Solved, obsolete.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2015, 08:16:48 pm
content: The first rule is: don't design for tight tolerances! When you look at RF chips you'll see the 50 Ohm impedance has quite a large spread as well. From my experiments using a dielectric constant of 4.5 is a close match between simulation with Sonnet Lite and real microstrip circuits.

author: KJDS
author_rank: Super Contributor
timestamp: October 04, 2015, 08:37:28 pm
content: I once put a design into production in three different continents at once. Fine in the UK, designed with 4.7, low in freq in Canada and high in freq in China.If it's critical, don't use FR4 unless you can trial it with a known good supplier then stick with that supplier.

author: tggzzz
author_rank: Super Contributor
timestamp: October 04, 2015, 09:29:58 pm
content: In a four layer stackup, the prepreg characteristics and thickness are more important.Don't forget FR4 is a poorly-specifiedwovenconstruction, so the impedance can vary depending on whether the track is on top of a weft or over the gap between wefts.
RF link for controlling the state of a relay/motor - Page 1
Forum section: electronics / projects

author: IoTguy
author_rank: Contributor
timestamp: November 28, 2024, 05:24:38 pm
content: Hi all,I'm looking for recommendations/ideas for an off the shelf RF solution.I'm working on a sensor logging system (let's refer to it as the logger) that has a volt free relay output that is used to turn on a motor in certain scenarios. My client now wants the logger to be battery powered in the middle of a small lake and have the motor on the lake bank (say 100 meters apart). This needs an RF solution that can send the desired state of the motor to something at the other end of the RF link so that the motor can be controlled. E.g. the state of the relay needs to be mirrored to the other end of the RF link.The common pulse based RF solutions (e.g. garage door control, lighting control etc.) won't fly here as they can get out of sync, there isn't a human involved here to "see" the state of the other end and keep pressing/pulsing the input until the desired state is achieved. It is important that the two relays stay in sync.In Addition to the relay output on the logger, there are some digital outputs and inputs (3V level) that could be used for this instead of the relay. There is a serial port (UART) too but unfortunately that is being used for something else otherwise that would be a good way to control an RF link. The logger is battery + solar powered so power consumption on the logger side of the RF link should not be too high.What would you recommend for this?

author: Poroit
author_rank: Frequent Contributor
timestamp: November 29, 2024, 04:08:39 am
content: G'day IoTguy,I have used these for past applications:https://defineinstruments.com/shop/wireless/twin-link-p2p-paired-nodes/
RF loss bridge design - Page 1
Forum section: electronics / projects

author: 84750Erik
author_rank: Contributor
timestamp: October 09, 2017, 03:31:41 pm
content: For a moisture sensor project I need to include a loss bridge. The purpose of this bridge is to measure variations in sensor capacitance. The sensor consists of a antenna inserted in soil, emitting a 100MHz signal obtained from a LTC6905 oscillator, and the measurement is done with a AD8307 logarithmic amplifier. The probe uses 2 insulated and waterproof parallel insulated copper strips; hence measurement is not done through electrical current but through electromagnetic fields.I found a design used in a commercial moisture sensor measuring emitted power, and a design used for regular RF antenna or load balancing using a reference load.For this project I presume both principles may be used, but I would like to receive your critical reviews on pro and con of each design principle.The first attachment shows the design for the commercial unit where IC1=AD8307, IC2=LTC6905, R1&R2=470R, C1&C2=10nFThe values for the other, second, loss bridge are marked on the drawing.What would/are be the pro and con for each design?What would be recommended for a circuit used to measure the impedance (and hence emitted power) of a probe consisting of two copper strips (insulated and waterproof covered) 10cm long, a few mm wide and a few mm apart, inserted in soil.