hybridfree/eevblog-posts huggingface dataset:
LM4871 vfd filament driver circuit issue - Page 1
Forum section: electronics / beginners

author: eriknau
author_rank: Newbie
timestamp: October 10, 2022, 05:30:50 pm
content: I have followedthis designfor a vfd filament driver circuit with the LM4871 chip specificallythis schematic. It works great in the breadboard providing a square wave at ~3kHz frequency and vfd segments are crisp while non-lit segments are completely dark. Then I moved the circuit to a 2-sided PCB I made on a CNC and I'm getting weird noise I can't identify. Lit segments are still bright but those segments are dimly lit across other grids where they should be turned off. I had the breadboard and PCB circuits powered at the same source, from the 3.3V pin on a Teensy LC that is controlling the segments through darlington transistor arrays. The only thing I can figure is I have connected something that's causing the noise in the pcb design.If anyone can see it I would be grateful for input!This is my version which I tried to make the same:and the PCB design:

author: Zero999
author_rank: Super Contributor
timestamp: October 11, 2022, 04:19:37 pm
content: What sort of capacitors are on the PCB version? Certain types of ceramics are piezoelectric which means they vibrate, when an AC voltage is applied. Try changing C2 for an aluminium of tantalum capacitor, or swap C1 and C2, assuming C1 is polarised i.e. not ceramic.

author: eriknau
author_rank: Newbie
timestamp: October 11, 2022, 06:57:53 pm
content: Thank you, that's a good tip. C1 is indeed electrolytic, C2 is ceramic and C3 I've swapped between ceramic disk and polyester. I will try some more swapping and see where it leads!

author: eriknau
author_rank: Newbie
timestamp: August 09, 2025, 06:34:36 pm
content: Took 3 years of on-and-off troubleshooting but I solved this issue! It turns out the breadboard provided enough resistance that the voltage across the filament was in the optimal range of ~3.3V for the filament/segment differential. Putting the circuit on a PCB lowered the resistance, increasing the voltage across the filament to ~5V, causing filaments to glow that shouldn't be. I added a 10 ohm resistor to one of the filament signal wires and the vfd looks great. One thing that threw me off was the PCB would power the filament effectively if I connected it to the circuit with alligator clips. Now I realize the alligator wires were adding resistance as well.
LM723 current limiting problem (PSU of SATT SAM 82 console) [solved] - Page 1
Forum section: electronics / beginners

author: argintviu
author_rank: Contributor
timestamp: February 06, 2024, 11:11:09 am
content: I have a few uA723 ICs that I'd like to use to make a bipolar +-15V power supply for a voltage reference. As a basis for the design I used the schematic of SATT SAM 82 console PSU which uses 2 x 723 and PNP pass transistors (lower noise). The nice thing is that it also has a current limiting feature which other implementations lack.Before making PCBs I simulated the circuit in LTSpice, but the current limiting feature doesn't seem to work. In the SAM 82 service manual, it says this:Quote from: SAM 82 manual, page 23In the simulation the limiting does nothing and the circuit pulls up to 2 amps from the supply (with both LM723 models that I found online). Now I don't want to try "live" because I fear that the 723 might get fried and they're pretty rare to come by these days (and also I have the TO-10 version which is hard to breadboard).What am I missing here? I doubt the circuit is bad since it was in production. Maybe the simulation models are bad? I have attached the original schematic and the simulation files.

author: Avelino Sampaio
author_rank: Frequent Contributor
timestamp: February 06, 2024, 11:28:31 am
content: There is an error in the simulation circuit. The 15v output and C6 must be connected between R6 and R4. All output current has to pass through R6, so that the LM723's current sensing transistor can act in protection.

author: argintviu
author_rank: Contributor
timestamp: February 06, 2024, 12:09:57 pm
content: Thank you for the help, it works now. I should have followed the original schematic's layout to keep mistakes like this out. Truly embarrassing.
LM723 Power Supply Problems - Page 1
Forum section: electronics / beginners

author: potatogun96
author_rank: Contributor
timestamp: July 02, 2014, 06:43:47 pm
content: I built a power supply based off of this design:http://www.eleccircuit.com/regulator-0-30v-5a-by-ic-723-2n3055-2part/After building the circuit and checking all my connections, I tested the circuit. The output remains constant, slightly over 30 volts. The LM723 started to heat up, and R4 also started to burn, so I replaced it with a 1k ohm resistor. The output is still constant, but the resistor is not burning like before.Are there any modifications I should make before replacing the chip with the extra LM723 that I have? I do not want to damage the remaining chip.

author: SeanB
author_rank: Super Contributor
timestamp: July 02, 2014, 07:09:03 pm
content: Remove Q1 and Q2, and short between pin 11 and the bases of the 2 power transistors. R5 can be 1k.You also have your pinouts wrong. Refer to the data sheet.http://www.ti.com/lit/ds/symlink/lm723.pdfSave the remaining 723, they are very nice chips.

author: potatogun96
author_rank: Contributor
timestamp: July 02, 2014, 07:22:17 pm
content: Thank you for the advice. I am new to power supply design, and didn't know where to even begin. I will throw the new circuit together on a breadboard and test before I start to desolder parts, but the new design makes sense.
LM723 regulator  - Page 1
Forum section: electronics / beginners

author: yashrk
author_rank: Frequent Contributor
timestamp: July 08, 2014, 04:18:19 pm
content: heyfriends,I am working on a project where I need current control regulator to drive leds (5W) and I came across LM723 which has current control inside, I understand how it works but I don't know how to design it for specific current value. I had a look on its TI datasheet but it didn't helped much. Please if some one can help me over this.If you know any more IC's with CC regulator in it and which is widely available, please do share. Thank You.

author: rolycat
author_rank: Super Contributor
timestamp: July 08, 2014, 04:37:20 pm
content: Hi yashrk.The standard LM317 can be used as a simple current source suitable for driving LEDs - there are details in the datasheet as well as many examples on the web.If your requirements are more complex, please provide some additional detail - it will help more knowledgeable forum members to provide better targeted assistance.

author: retrolefty
author_rank: Super Contributor
timestamp: July 08, 2014, 05:01:06 pm
content: LM317 is much simpler to implement a CC source compared to the 10 pin LM723. Also the LM723 cannot control much current without external power transistor.
LM741 Inverting Amp - Page 1
Forum section: electronics / beginners

author: Legion
author_rank: Frequent Contributor
timestamp: April 03, 2014, 03:17:31 am
content: I've got the following inverting amp:I set the supply voltages at +-6V. But the negative supply keeps hitting the overcurrent protection on my supply. OCP is set to 150mA and the negative rail barely exceeds -2V before hitting the current limit. I'm a little wary of increasing the limit since the datasheet says max power dissipation is 500mW and it's already at 300mW.I've got my FG hooked up to Vin. My scope is hooked up to Vinon channel 1 and Vouton channel 2.The scope shows the 5Vpp 1kHz signal coming from my FG on channel 1. The output from the LM741 is on channel 2. Channel 2 shows 0V during the positive swing and a ramp to 4V during the negative swing. The output looks like the skewed top half of a sine wave at lower Vin.I'm not sure why the negative supply is trying to sink so much current. I've re-breadboarded the circuit multiple times and checked the breadboard for shorts. I swapped the LM741 IC for another one and get the same thing. Measured my resistor values on my DMM and they're well within spec.

author: Silverio
author_rank: Newbie
timestamp: April 03, 2014, 05:26:13 am
content: I've tried the circuit you described and with no load my negative rail pulls only 3mA. I would try testing the Opamp by itself with no other connection but the power supply rails to see if the problem is the IC or the wiring of the other components.

author: Unknown
author_rank: Unknown
timestamp: April 03, 2014, 07:56:43 am
content: Which version (e.g. LM741/A/C/etc)? Reputable manufacturer, possible fakes, or chinese specials? Does it work if you increase the supply rails?I ask because the LM741 is poorly-spec'd at low supply voltages - although it's generally considered to function down to +-4.5v and some versions are characterised from +-5v up, they're pretty shitty at that. I bought some years ago that were no good under about +-7v.And your FG is AC-coupled to your circuit, right?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 03, 2014, 03:08:45 pm
content: Wrong pinout, or backwards, or just completely toast. Try again, new chip, check every single connection.

author: Legion
author_rank: Frequent Contributor
timestamp: April 03, 2014, 09:33:37 pm
content: I figured out the problem. I was grounding the two offset pins on the premise of them being unused "inputs". This must have acted like a short. I realize now that I neglected to mention the offset pins in my original post. My bad.
lm741 op amp no gain - Page 1
Forum section: electronics / beginners

author: funkimunky
author_rank: Contributor
timestamp: October 22, 2012, 09:45:57 am
content: I am learning to use the lm741 op amp but I cannot get any gain, in both the non inverting and inverting setup. I can get the signal to invert but the most I can get is about 1 to 1. I have the op amp powered by a switching benchtop power supply set at 18v and put through voltage divider (2x 100ohm) so I can get +9v 0v and -9v. The voltage divider has some 220uF caps to clean the signal. I am using a cheapo signal generator built for £5.00 powered by a 9v battery that outputs a sin wave of 500mV max. The output is connected to the non inverting input on the op amp while the ground is connected to the 0v rail of the voltage divider.I have tried to adjust the power supply to see where the gain maxes out when it is the same as the input signal. This happens when the power supply is set at 4.4V or +2.2 -2.2.Can anyone help me figure out why this is not working as I now have no Idea where to try.I have attached a diagram of my setup.

author: poptones
author_rank: Frequent Contributor
timestamp: October 22, 2012, 09:49:36 am
content: You're trying to drive a ten ohm load. Look at the resistor divider chain in the feedback loop. It takes a mighty powerful opamp to drive ten ohms with any appreciable gain. Change the ten ohms to 5K, change the other to 50K.

author: Rerouter
author_rank: Super Contributor
timestamp: October 22, 2012, 09:50:44 am
content: you have it miswired, your just shorting the output through the 10 ohm, you want it on the other side of the 1K to the inverting input, to divide the voltage on that pin,

author: funkimunky
author_rank: Contributor
timestamp: October 22, 2012, 10:34:39 am
content: Thank you its all working as expected now. Its obvious now that you have shown me what the mistake was.
LM741 op-amp - Page 1
Forum section: electronics / beginners

author: selim
author_rank: Newbie
timestamp: December 07, 2022, 05:42:36 pm
content: I know that in ideal-opamps the resistor Rs has no effect. But what is the purpose of using the Rs resistor in the circuit for LM741? Will there be any change if we increase or decrease the resistance Rs?

author: rstofer
author_rank: Super Contributor
timestamp: December 07, 2022, 06:16:04 pm
content: https://electronics.stackexchange.com/questions/570426/why-put-a-resistor-in-series-with-the-positive-terminal-in-a-non-inverting-op-am

author: Zero999
author_rank: Super Contributor
timestamp: December 07, 2022, 07:22:36 pm
content: RSshould be 800R, the nearest E24 value is 820R, but 1k is close enough. Actually, with these low values, it doesn't matter, because the bias current is small enough, the additional offset will be way below the 741's offset voltage.

author: TimFox
author_rank: Super Contributor
timestamp: December 07, 2022, 10:40:17 pm
content: At low resistances, as pointed out above, the bias-current cancellation is rarely important when you do the arithmetic.However, the 1k resistor on the + input may provide some protection against overvoltage (not much), since it will limit the current into the pin when the input voltage exceeds the common-mode range, or the voltage at the - input when the output reaches maximum.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 09, 2022, 03:09:15 pm
content: As noted, it helps reduce the effects of input bais currents.In many appications this doesnt matter much becasue modern GP opamps tend to have very low bias currents.Its good idea to add Rs in high gain and temperature sensitive applications.If your feedback currents are of the same order as Ib, watch out!RF, Video and Audio opamps designed for low impedance and low noise circuits may have very high bais currents.
LM7555 Monostable Trigger  - Page 1
Forum section: electronics / beginners

author: Xenos
author_rank: Contributor
timestamp: February 27, 2022, 11:14:51 am
content: Hello,When configuring an LM7555 in monostable mode, as shown on the schematic, is there a method to make the pressing of the button a momentary event, no matter how long the button is held down? In the circuit shown here, the LED will stay illuminated as long as the switch is closed. Only after releasing the button will the timer begin. In my project, in lieu of the button, I have an IR break-beam that triggers a LM393, which in turn energizes a transistor that triggers the LM7555. The issue is that as long as the beam is blocked, the output of the LM7555 is active.An analogy would be how some doorbells ding when you hold the button, then dong when you release it. I would like to make it so when the button is pressed and held, the doorbell does a full ding-dong cycle. Essentially, the button press automatically resets the trigger, until it is pressed again.Thanks in advance!

author: jpanhalt
author_rank: Super Contributor
timestamp: February 27, 2022, 11:36:21 am
content: Yes, use a capacitor in the trigger circuit. Example attached.EDIT:And another example of the same approach from the Paisley site (attachment 2).

author: Xenos
author_rank: Contributor
timestamp: February 27, 2022, 07:56:15 pm
content: Thank you very much!
LM75ADP,118 and SI5351A-B-G under PSOC4 control  - Page 1
Forum section: electronics / beginners

author: analityk
author_rank: Regular Contributor
timestamp: June 05, 2025, 02:42:31 pm
content: Hey folks.I came across a problem and so far I haven't found a better solution, take a look at the code.I have two chips on the I2C bus. One is a PLL the other is a temperature sensor.As long as I first tried to talk to the LM75 then the SI5351A chip did not work and the LM75 did not work properly.Then I swapped this order and it turned out that SI5351A works perfectly but as I started communicating with LM75 the whole thing stopped working.Strange?The problem was solved only when I added a hardware reset of the i2c bus after setting the pointer on the LM75.The GPT chat insisted on waiting indefinitely for the bus state to return to IDLE mode but only I2C_Stop() was able to do that.I wanted to ask you guys if anyone has had such problems with the LM75 or if I got a fake one (I ordered the assembly service from jlcpcb).So far the CY8C4245 (CY8C4245LQQ-483) uC has worked with many chips on i2c and this is the first time I've run into problems.Code:void lm75_read_temp(LM75R* t){if(t != 0){uint32_t result = I2C_I2CMasterSendStart(t->addr, I2C_I2C_WRITE_XFER_MODE, TIMEOUT);result |= I2C_I2CMasterWriteByte(LM75_R_TEMP, TIMEOUT);result |= I2C_I2CMasterSendStop(TIMEOUT);I2C_Stop();CyDelay(100);I2C_Start();CyDelay(100);result |= 0x10 * I2C_I2CMasterSendStart(t->addr, I2C_I2C_READ_XFER_MODE, TIMEOUT);result |= 0x10 * I2C_I2CMasterReadByte(I2C_I2C_ACK_DATA, &(t->reg_temp_msb), TIMEOUT);result |= 0x10 * I2C_I2CMasterReadByte(I2C_I2C_NAK_DATA, &(t->reg_temp_lsb), TIMEOUT);result |= 0x10 * I2C_I2CMasterSendStop(TIMEOUT);t->i2c_fault = result;};};

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: June 10, 2025, 08:06:55 am
content: If you have a logic level analyzer, check if Si5351A or LM75 holds SDA low during boot.
LM7805 Backfeed Protection - Page 1
Forum section: electronics / beginners

author: NateT94
author_rank: Newbie
timestamp: February 19, 2021, 11:16:06 am
content: Hi,I am a beginner in circuit design and had a question about back-feed protection for an LM7805 voltage regulator.The circuit I am designing contains multiple IC's and an Arduino that are all powered from a 5-volt rail that comes from an LM7805.I would also like to add a USB connection so that I can program the Arduino. The 7805 will not be supplying power while the USB cable is attached, the 5-volt rail will be powered through the USB cable.My question is, what is the best method for protecting the LM7805 from back feed voltage when the 5v rail is being powered over the USB cable.My first thought was to simply put a diode on the 7805's output, but that would drop the regulated voltage so it's not optimal.Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2021, 11:18:03 am
content: Put a diode between the LM7805's output and input.

author: NateT94
author_rank: Newbie
timestamp: February 19, 2021, 11:23:52 am
content: The 7805 would normally be powered by a 12v wall wart, however, if the 12V supply is disconnected while the USB is connected, then where exactly would the diode be directing the voltage?I don't really understand how that would protect it.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: February 19, 2021, 12:59:06 pm
content: I'm not sure the diode's needed unless you're running high output voltage(which 5v isn't) and a 10uf+ output capacitor. Not sure if that recommendation extends to external 5v power while the 7805 is still connected but off though.

author: ledtester
author_rank: Super Contributor
timestamp: February 19, 2021, 01:04:45 pm
content: Quote from: NateT94 on February 19, 2021, 11:23:52 amThe diode is used as described in sections 8.1.1 and 8.1.2 on page 13 of the TI's datasheet:https://www.ti.com/lit/ds/symlink/lm7800.pdfQuote

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2021, 01:22:54 pm
content: Quote from: NateT94 on February 19, 2021, 11:23:52 amThe current would be directed to the LM7805's input. It won't do anything, except for draw a small current.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 19, 2021, 01:26:29 pm
content: The data sheet tells all!

author: NateT94
author_rank: Newbie
timestamp: February 19, 2021, 01:48:54 pm
content: That makes sense. Thanks everyone.It seems so obvious now haha.

author: Noise0
author_rank: Contributor
timestamp: February 19, 2021, 02:19:27 pm
content: Quote from: NateT94 on February 19, 2021, 11:16:06 amUsually i dont disconnect external power when usb is connected.Usb connection is usefull not only to program it but even to get some serial print for debug or logging.This way you don't even have to worry about back feed issues.
LM7812 or ??  - Page 1
Forum section: electronics / beginners

author: spiwrx
author_rank: Newbie
timestamp: February 14, 2024, 07:19:10 pm
content: I'm looking at retrofitting a small LED panel to old incandescent fixture. The source is 12vac landscape light transformer that I cannot change. Actual voltage is closer to 11vac.The panel I have works directly off 12vdc (10watt). I put a full wave rectifier on there but the voltage drop is too much, the panel barely glows. Using my DC bench supply 12vdc directly to the panels lights as designed. I can add a capacitor but considering a voltage regulator which I don't have experience with for space savings.My question is, do I need to clean up the ripple on the simple full wave rectified AC, or can I feed it will simple rectified voltage directly.I don't have enough room to add both capacitor and regulator. Looks like the LM7812 will suit my needs (12v 1.5a)

author: wasedadoc
author_rank: Super Contributor
timestamp: February 14, 2024, 07:33:58 pm
content: The full wave rectifier only turns the negative half cycles of the sine wave into positive ones. Will still have significant periods of time every 8.4 ms where the voltage is very low. That is why the reservoir capacitor is needed. Applying 11 Volts RMS to rectifier plus capacitor is likely to produce an output around 15 Volts DC. If that is too high for the display you need the regulator. A linear one such as a 7812 converts the excess voltage into heat. Depending on the current taken the 7812 may require a heatsink. 10 Watts from 12 Volts is almost 1 Amp so close to 3 Watts dissipated by the 7812. Definitely need heatsinking.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2024, 08:02:32 pm
content: The 7812 can only ever reduce the voltage, not increase it, because it is a linear regulator, which burns off the additional voltage as heat, as mentioned above.Try adding a smoothing capacitor, but my advice is to buy an LED light designed for 12VAC.

author: spiwrx
author_rank: Newbie
timestamp: February 15, 2024, 06:56:51 pm
content: This make sense. I saw the input range was like 9-15v and thought there was hoping it would do minor compensation.

author: Zero999
author_rank: Super Contributor
timestamp: February 15, 2024, 07:45:24 pm
content: Does the enclosure prevent the user from touching it? If so, then how about using a mains lamp and a small transformer to boost the voltage back up to 120V and use an ordinary mains light? A 9V transformer run in reverse will give 120V out, under load.Note the reason why I suggested a 9V transformer, is because the secondary has extra turns to compensate for the drop under load and your voltage is 11V, not 12V. Ideally get one designed for both 50Hz, as well as 60Hz, then the extra voltage will be even less of a problem, as it's fine to run a 50Hz transformer at a slightly higher voltage on 60Hz. The obvious downside is it's not so safe, but you've still got the benefit of isolation.

author: tooki
author_rank: Super Contributor
timestamp: February 16, 2024, 06:57:46 am
content: Quote from: spiwrx on February 15, 2024, 06:56:51 pmThe input range of what? Certainly not of a 7812.
LM78L 05 ACZ - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: June 03, 2023, 12:42:26 am
content: Guys how can I test this correctly? I put in a cheap Chinese transistor tester and it shows the following as seen in picture.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 03, 2023, 01:17:06 am
content: Those testers can't check a LM78L05... Because it's not a transistor, FET, diode, capacitor, resistor, etc.They don't check IC voltage regulators, which is what a LM78L05 is.

author: Crambone
author_rank: Frequent Contributor
timestamp: June 03, 2023, 02:08:36 am
content: OK thanks I figured it wasn’t testing it correctly. I tested voltages in circuit and it’s working properly after I found a 100uf cap that tested 17uf.

author: barshatriplee
author_rank: Regular Contributor
timestamp: June 03, 2023, 07:54:37 am
content: The easiest way to check these voltage regulator ICs is to use a multimeter and a DC power supply. Give the appropriate input voltage according to the datasheet. And see if you are getting the desired output voltage in the output pin.

author: Zero999
author_rank: Super Contributor
timestamp: June 03, 2023, 11:31:30 am
content: Quote from: Crambone on June 03, 2023, 02:08:36 amWhat made you think the tester wasn't working? It's a transistor tester, yet the L78L05 is a voltage regulator, an integrated circuit, not a transistor. The only way to test it is to build a circuit with it.

author: Jwillis
author_rank: Super Contributor
timestamp: June 03, 2023, 05:26:18 pm
content: Its an honest mistake to make for beginners. Package design can throw off a novice if they are not familiar with the numbers on the component or with data sheets that may be supplied. even understanding what the data sheet is saying can be a challenge for a beginner.I did a quick search for the component LM78L 05 ACZ and found this for youhttps://www.ti.com/lit/ds/symlink/lm78l.pdf?ts=1685812998671&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM78L%252Fpart-details%252FLM78L05ACZ%252FNOPB. The numbers can be slightly different based on the type of package but essentially function the same way. The data sheet will often show you a basic functional circuit.Good luck and have fun.

author: donlisms
author_rank: Frequent Contributor
timestamp: June 05, 2023, 02:40:44 am
content: And... some component testers recognize voltage regulators, though I can't remember which one(s)! It may have been mentioned in a comparison of the Peak tester and some other. Sorry. But I know I didn't imagine it... :-)

author: Jwillis
author_rank: Super Contributor
timestamp: June 05, 2023, 04:46:47 am
content: Quote from: donlisms on June 05, 2023, 02:40:44 amI believe the TSH-06F Integrated Circuit IC Tester does. Linear regulators only like the 78XX series.
LMM84 LCD Display, cant find datasheet [SOLVED] - Page 1
Forum section: electronics / beginners

author: J.Tax
author_rank: Contributor
timestamp: January 22, 2016, 09:51:27 am
content: Hello,Recently I bought a box packed with electronics. Inside the box there was a LMM84SA19C2E LCD Display from Nan Ya Plastics Corp.The problem I'm having is that I cant find any datasheet of the display. Does somebody know where I can get the datasheet?I have included some pictures of the front and the back.Back:http://nl.tinypic.com/r/2vkkgmf/9Front:http://nl.tinypic.com/r/2vdk2n4/9With dear Kinds,J.Tax

author: newbrain
author_rank: Super Contributor
timestamp: January 22, 2016, 10:16:58 am
content: From the pictures, it looks very much like any other Hitachi HD44780 based 2x16(?) display.Plenty of resources on the web, e.g.http://www.spikenzielabs.com/SpikenzieLabs/LCD_How_To.htmlIt probably has got LED backlight and doesn't need a negative Vee (as older models did), but the best way to determine this is to try...

author: J.Tax
author_rank: Contributor
timestamp: January 22, 2016, 11:06:59 am
content: Quote from: newbrain on January 22, 2016, 10:16:58 amThanks. It works like a charm
LMS350GF10 display datasheet - Page 1
Forum section: electronics / beginners

author: vamp666
author_rank: Newbie
timestamp: October 18, 2014, 02:25:14 pm
content: Hello.Anyone have or can find this Samsung display data sheet? I tried Samsung, Google and some datasheet archive sites with no luckI got this display from an old gps.It appears is discontinued.

author: amyk
author_rank: Super Contributor
timestamp: October 18, 2014, 03:10:51 pm
content: What do you need to know about it?Fromthis imageI could find of the FPC, the signal names show a pretty conventional parallel-interface LCD; the LMS350GF21might be a close match, and there is a datasheet for that one:http://www.wayengineer.com/download/SAMSUNGpdf/LMS350GF21.pdfEdit:LMS350GF08datasheet is also very similar.

author: sunnyhighway
author_rank: Frequent Contributor
timestamp: October 18, 2014, 03:15:18 pm
content: Looks like the LMS350GF10 is a member of the Samsung LMS350GF range with roughly identical properties:http://www.panelook.com/modelcompare.php?ids=7177,11922,7176,7175,7174,7173,7172,7171,7170,7169,7168,20852,7167,7166,7165,7164You could try this spec sheet.http://www.beyondinfinite.com/lcd/Library/Samsung/LMS350GF03-001.pdf

author: vamp666
author_rank: Newbie
timestamp: October 20, 2014, 01:51:06 pm
content: Thank you both for replay.I need to know the pinout for this display.Mine have 45 pins, but your alternatives all have 71 pins.it seems the best match is GF13 and GF12, but again.. no datasheet. uhh...From the info on the flatflex, i can tell pins 1 and 2 are led, 3 is GND etc. But after i count them, i am short 6 or 7 pins.I see the SDO marking, but i cant tell witch pis is it. The flatflex is multilayerd.

author: godFather89
author_rank: Contributor
timestamp: October 20, 2014, 01:59:40 pm
content: It seems to be a plain parallel (24 bit maybe), 320x240 lcd with touch screen?Why do you need the pinout? Do you plan on using it? With a FPGA or do you have a controller?Similar LCDs (with documentation) can be found cheap.
LMX2322 prescaler - Page 1
Forum section: electronics / beginners

author: smbaker
author_rank: Regular Contributor
timestamp: December 19, 2015, 09:51:27 am
content: Working on a frequency counter project and trying to use an LMX2322, datasheet athttp://datasheet.eeworld.com.cn/pdf/193228,TI,LMX2322.pdf,and don't understand how I'm programming it wrong. There's a handful of projects on the web that use the LMX2322 as a prescaler, and that's where I got the idea.According to the datasheet:QuoteP is fixed at 32. I've set A to 0 and B to 8. According to the datasheet, these are valid values for A and B.By my calculations, it should be dividing the input signal by 33 zero times and then dividing by 32 eight times. This would be an overall division by 256. However, when I actually prototype the circuit out, I'm seeing the signal divided by 8. A 1 Mhz input signal is yielding a 125 Khz output signal. What am I misunderstanding about the data sheet? As far as I can tell, divide-by-8 isn't even a valid configuration of the chip.Thanks,Scott

author: daqq
author_rank: Super Contributor
timestamp: December 19, 2015, 10:51:10 am
content: According to the datasheet (page 4), the minimal RFIn frequency is 700MHz, and the oscillator 5MHz. Where are you putting this 1MHz in?

author: smbaker
author_rank: Regular Contributor
timestamp: December 19, 2015, 04:41:08 pm
content: Well that may explain it... That's the sentence in the datasheet I must have missed!I'm applying the 1 Mhz to the Fin pin via a 1nf capacitor. The circuit I've constructed is very similar to the one described here:http://hem.bredband.net/noda/freqmanual.pdf.I'm using a different CPU (a parallax propeller) and I'm driving it from 3.3V. This particular project claims to work down to 5 Mhz. I have tried injecting signals as high as 16 Mhz into mine, and still get the divide-by-8 behavior. I don't have the cp_out line connected to a microcontroller, but rather have it going to my scope and/or frequency counterI suspect they're not using the chip for it's intended behavior and maybe this is how they're operating it out of the datasheet's stated range -- they're not using the oscillator circuit at all, and are using it only as a prescaler based on the N counter. Code that I found in github suggests they operate the device in test mode (TEST=1, CP_TRI=1, PD_POL=1).The output when observing with the scope is noisy. I'm wondering if shoddy construction technique in my prototype is to blame, and input noise is being detected and triggering the counter.Scott

author: smbaker
author_rank: Regular Contributor
timestamp: December 20, 2015, 12:46:54 am
content: Turns out it was poor construction technique. I rebuilt the circuit, and it's working fine, dividing by 256 with input signals as low as 5 MHz. Below 5 Mhz, it starts to get kinda wonky.
Lo Vce Equivalent replacement for ULN2003 - Page 1
Forum section: electronics / beginners

author: whizgeek
author_rank: Newbie
timestamp: March 15, 2018, 12:27:22 am
content: Hi All. First off, I'm new registered to post but longtime lurker.A 5v application, uses one of these 2003 open collector drivers for a bunch of relays.New design puts a green(ish) smps to power the whole circuit.But the 2003 has a Vce Sat of >0.85V in this application, add in a drop for power filtering etc, and the resulting drop is too high to reliably drive the relays.So ideally need a pin-pin compatible 7channel lo side driver/switch with low Rds/VsatHave looked at TPL7407 - 5v is too low. TBD62003 has similar Vds to 2003..Anyone any other suggestions?

author: helge
author_rank: Regular Contributor
timestamp: July 23, 2018, 03:38:31 pm
content: Mildly disappointed by TPL7407 and its "internal LDO".TPL7407: 8.5V minimum VCOM (misnomer, should be VCC) with an LDO to 7V which turns out dying when subjected to >0.5V/µs, so don't use the internal freewheeling diodes. Oh lord...Now evaluating TPL7407LA (starting at 6.5V and with internal regulation to 5.3V) vs. ULN2003LV.

author: exe
author_rank: Unknown
timestamp: July 23, 2018, 05:28:13 pm
content: Why not using a logic-level mosfets (descrete or arrays)? Just don't forget protection diodes, etc.

author: bson
author_rank: Unknown
timestamp: July 24, 2018, 01:10:11 am
content: You can always use a dual switching MOSFET, like Diodes IncDMG6898LSD. At Vgs=2.5V and Id=8.9A, Rds<=23mohm. Since Rds is PTC at smaller currents the max channel resistance will be lower and Vds lower as well; fig1 in the datasheet suggests Vds<<100mV @ Id<1A currents. The drawback of the DMG6898LSD is the rather large 50mil SO package, but you could probably fit 3 of these within the real estate of one ULN2003, and get other benefits like placement closer to the relays and more distributed heat dissipation if you need significant switching currents. If you switch using GPIO pins on a µC this combined with pin swapping can simplify layout.Or maybe a quad/hex/octal common-source variety - if you can find one with high channel on-conductance (~>25S). If you do, let me know! With independent S pins you can use a source resistor to set the driving current and reduce noise and glitch sensitivity (always a good habit when dealing with relays, even with flywheel diodes), but may not need this if the coil supply voltage is a good match for the relay.There are also low-Vce(sat) BJTs, but I'm only aware of discrete devices, not any sort of array, but this may be your best bet if you need TH. You could easily make a small adapter board with a few of these that is pin compatible with a ULN2003. (But if you do this you might as well use modern SMD parts IMO.)
Load capacitors, MCP79410 with attiny and whatnot - Page 1
Forum section: electronics / beginners

author: Moriambar
author_rank: Unknown
timestamp: April 09, 2019, 11:04:45 am
content: Hi.After a long time I'm here to discuss one of my long term failed projects, from which I'd like to learn.I used anmcp79410 RTCCwith an attiny85 to have basically something activated on calendar based events.The problem is that I was never able to provide the correct load capacitors for the 32.768kHz crystal, no matter what the design.I was basically using a 9pF crystalfrom citizen, and calculated that for the given 3pF capacitance of the pins, 3pF of stray capacitance from the pcb (I read that 2-4pF is usually a suitable value, I don't know how to calculate that precisely), I should use two 6pF capacitors to obtain the 9pF total load capacitance.I tried several boards mixing 6 and 7 pF capacitors, trimmed the frequency but found out that no matter what I do the clock always seems to be off calibration (out of minutes in a month).I know this post is perhaps a bit confused (that's why I posted it here and not on the design forum), but can you please help me on how to face this problem properly and obtain a good result with the mcp79410?ps: I run from battery,3xAAcheers

author: mvs
author_rank: Frequent Contributor
timestamp: April 09, 2019, 02:41:00 pm
content: Quote from: Moriambar on April 09, 2019, 11:04:45 amCheck your mathCL=(Cx+Cosc)/2+CstrayCL=(6pF+3pF)/2+3pF=7.5pFQuote1 minute in a month is around 23ppm... Depending on environment temperature change, initial aging, etc... it might be even in spec.PS Have a look at RTC with integrated temp compensated crystal, like DS3232M. +/-5ppm in -40/+85* C range and no mess with load caps.https://datasheets.maximintegrated.com/en/ds/DS3232M.pdf

author: Moriambar
author_rank: Unknown
timestamp: April 09, 2019, 02:55:37 pm
content: Quote from: mvs on April 09, 2019, 02:41:00 pmThanks. I now finally understand the formula, so basically for 9pf I shoud put there 9pF capacitors, right? (9pF+3pF)/2+3pF=9pF (assuming 3pF is good as an estimate on the stray capacitance).I will definitely check out RTCs with integrated compensated crystals, I hope to find the right one!ps: the number I gave where after trimming done in the RTC79410 (which is ~127ppm), so the actual factor was ~150ppm (127 + 23 since they had the same sign).Cheers
Load Cell measuring and info display - Page 1
Forum section: electronics / beginners

author: BoomENGR
author_rank: Newbie
timestamp: February 19, 2019, 05:10:00 pm
content: Hey, I am a college student working on designing and building a rocket thrust tester.I need an affordable load cell and a way to display the information on a force vs time graph on my laptop.The rockets will be produceing around 10 to 14N of thrust.I need it to have a fairly high readings per second.Any suggestions will be appreciated, thank you!

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 19, 2019, 10:23:10 pm
content: I think 1 reading every 2 minutes is "farily high".What do you think is "fairly high"?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 20, 2019, 01:36:27 am
content: Bit more serious answer.HX711 is a very popular and cheap chip and it can sample your signal at a rate of upto 80sps.A lot of simple kitchen scales have a loadcell in them in the form of an aluminimum bar with holes & wires.https://duckduckgo.com/?q=loadcell+hx711&iar=images&iax=images&ia=imagesADS1220 or ADC1115 or similar chips might increase your resolution / measuring speed.https://duckduckgo.com/?q=ADC+PGA+SPI&iar=images&iax=images&ia=imagesAlso plenty of mechanical examples from youtube vids and complete sourcecode from github.
Load Line technique to intersect two dynamic electrical components? - Page 1
Forum section: electronics / beginners

author: killingtime
author_rank: Regular Contributor
timestamp: October 24, 2023, 04:13:51 pm
content: Hi,Is it possible to use the load line technique to work out the current in a series circuit comprising two dynamic components?The load line method is normally used with one dynamic component and a linear component like a resistor. Example below.The only examples I can find on-line are for the above scenario. Nothing for two non-linear components.The resistive component isn't plotted as originating from the zero point, but starting from Vdd and mirrored around Vdd/2 on the x axis.If the linear component is replaced with another dynamic one would the same method work? Example below:In the above example we have an incandescent bulb in series with a battery and a constant voltage source (a charger). I understand the VI curve will vary for the battery as it charges, but I'm only interested in the initial battery state (discharged) which means I can work with one VI curve for that component.I've plotted the VI of both on the chart below. Blue line is the incandescent bulb. Red is the battery. Green is is the battery mirrored around Vdd/2 given Vdd=14.4v, so the mirror point is 7.2v.Maths as follows:Battery starts to draw current at 11.0vVdd/2 = 7.211 - 7.2 = 3.8v7.2 -3.8 = 3.4So the mirrored battery plot starts at 3.4v, and that would put the current at around 0.55A which is where the plots intersect.Thanks.
Load Resistors for power output measurement - Page 1
Forum section: electronics / beginners

author: Oleenick
author_rank: Contributor
timestamp: May 31, 2019, 10:17:24 am
content: Hello, EEVblog Forum.I was getting a bit confused about load resistors for power output measurement.Specifically, I'd like to measure the power output of a DC motor at different speeds.I know I can measure the voltage, should I use a load resistor? Why would I use one?My thought process lead me to thinking that the load resistor would also act as a current shunt.If I use a 10Ω resistor as a load I can measure the voltage across that.Does this also mean that this load is also a current shunt which will give me the voltage with when divided by 10 is the current?I could definitely be mistaken here, I just need someone to clear this up.Thanks!

author: mikerj
author_rank: Super Contributor
timestamp: May 31, 2019, 11:23:05 am
content: You cannot measure the poweroutputof a motor using a resistor, for that you need some way of measuring RPM and torque (i.e. a dynamometer).A resistor can be used to convert a current into a voltage, so you can indirectly measure the current with a voltmeter. By measuring the voltage across the motor and the current passing through it, you can calculate the powerinputto the motor, which is not the same thing as the power output (motors are not 100% efficient).
Load testing USB PD power bank / PSU - Page 1
Forum section: electronics / beginners

author: artv
author_rank: Contributor
timestamp: January 17, 2024, 03:06:45 pm
content: HiI have a Kunkin KP184 DC load tester. I want to use to apply a load to a USB-C PD power bank for testing.I have various USB testers that I can set to trigger various voltages via PD or QC. I'd like to wire up a USB-C (male) to + and - banana plugs or similar. If the USB tester is setting the voltage trigger I select, do I just need to connect Vbus and GND from a USB connector (with a breakout board?) to those respective two wires and plug that into my load tester. Or do I need to mess with the CC connections? Very unclear on this.I want to be able to test up to 28V, 5A (140W). If I go the break out board router, a lot of the USB-C break out boards only seem to support 3A? Not sure if that's related to the E-marker limit?I guess I could use a seperate PD trigger board which already has a + - output - I guess that would work ok for my needs? But ideally I'd like the control of selecting exactly the voltage I want using my USB tester in trigger mode.Hope that makes sense. Any help hugely appreciated!Thanks.

author: liaifat85
author_rank: Regular Contributor
timestamp: January 18, 2024, 12:52:42 pm
content: Focus on Vbus and GND connections for basic power supply, and use the CC lines if necessary for specific PD negotiation. If your USB tester provides the control you need, you might not require additional PD trigger boards.

author: radiolistener
author_rank: Super Contributor
timestamp: January 18, 2024, 01:09:28 pm
content: The main issue with testing PD chargers and power bank is to use good enough quality cables and connectors. Since they needs to pass 100 Watt power with 5 Amps current, you're needs really thick wires in the cable and very good quality high current USB connectors. Most of cables and most of cheap connectors and connector-adapters are not suitable for this.I suggest this PD trigger for testing, it works good with 5 Amps current:https://www.aliexpress.com/item/1005003828144045.htmlit has selectable PD voltage which you can set with onboard switches.You're also needs very good quality 100W USB-C cable with electronic mark.I recommend to buy at least UGREEN brand 100W cable or something better.Don't buy USB cable Baseus or noname brands, they have high voltage drop due to thin wires and bad connectors and very unreliable.PS: forgot to say, don't buy cheap USB power meters, they don't cost their money, because they have high voltage drop and high measurement error.

author: artv
author_rank: Contributor
timestamp: January 19, 2024, 09:04:21 am
content: Thanks.I think I was over complicating this - I just cut a 100W USB-C cable and connected red and black to my load tester, triggering off my USB tester. Worked perfectly!I have a few USB testers - all decent ones I use them all the time.Quote from: radiolistener on January 18, 2024, 01:09:28 pmI actually have this exact trigger board - except paid 10 times that off Amazon because I'm too impatient!Thanks again both of you.
Loading caps on crystals.  - Page 1
Forum section: electronics / beginners

author: hamster_nz
author_rank: Super Contributor
timestamp: September 14, 2019, 07:57:57 am
content: I have a newbie building a digital clock tomorrow, and am looking for a simple explination for the loading caps on the 32.768kHz crystal. It is the only part that I don't have a simple explination for.The best I can come up with is:They act as the electrical equivilent of springs at either end of a beam, encouraging the crystal to vibrate correctly.If these `springs` are too soft or too firm it dampens the oscillation rather than helping it.Does this sound about right/simple enough? Anybody got anything simpler?

author: Rerouter
author_rank: Super Contributor
timestamp: September 14, 2019, 08:04:40 am
content: the oscillator for a crystal is built to be as efficient as possible in order to accomplish this its built to work best in only a certain narrow capacitive loading range, The capacitors are used to trim this loading for all different crystal capacitance values.What it is specifically doing is adjusting the phase shift on the inverter so that it is very close to 180 degrees.

author: hamster_nz
author_rank: Super Contributor
timestamp: September 14, 2019, 09:07:42 am
content: Quote from: blueskull on September 14, 2019, 08:09:48 amYes, much better!

author: tooki
author_rank: Super Contributor
timestamp: September 14, 2019, 02:09:40 pm
content: Quote from: Rerouter on September 14, 2019, 08:04:40 amThis is a great example of a reply that might be technically correct*, but iscompletely and utterly uselessto a beginner (we are in the Beginners forum!). The OP made it clear they were trying to understand an analogy.Also, punctuation helps. Please use it.*I can't judge it, since I don't understand crystal oscillators, either.

author: wilfred
author_rank: Super Contributor
timestamp: September 14, 2019, 02:28:59 pm
content: I found the App note from Freescale. It might be of interest.https://www.nxp.com/docs/en/application-note/AN2606.pdf"Practical Considerations for Working With Low-Frequency Oscillators"

author: magic
author_rank: Super Contributor
timestamp: September 14, 2019, 06:54:02 pm
content: Quote from: hamster_nz on September 14, 2019, 07:57:57 amNot exactly, it shifts the resonant frequency a bit.Load capacitance needs to be as specified in order to obtain exact frequency.