Simplified Transistor Tester - Page 1
Forum section: electronics / testgear

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 15, 2025, 10:17:44 pm
content: Hello everyone,I have decided to build my own Transistor Tester. There are commercial variants from China, which are also quite cheap, but the quality is questionable and the user's control over the device is limited; for example, sometimes these devices cannot be updated to the latest possible firmware.So I looked at the DevKit-644 variant based on the ATmega644 chip, created by one of the authors of Transistor Tester's firmare. However, I found the original circuit too complicated and too expensive, so I decided to optimise it. My idea is to simplify every possible part of the design as long as it doesn't significantly reduce the precisionby minimising the number of components,by replacing more exotic components with more common ones,by replacing expensive components with more inexpensive ones, andby minimising component variations (e.g. only one type of NPN or PNP transistor).A.The greatest optimisation can be made in power management. The original design assumes the use of both a battery and an external 7-12 V power source and is therefore designed to minimise power consumption. However, I think that both batteries and higher voltage sources are impractical compared to the ubiquitous USB chargers. Therefore, my original goal was to power the device with a 5V USB power source only.I debated at length whether a typical switching regulated USB source would be suitable for such a precise device. In fact, typical devices have aripple voltageof about 50mV at frequencies well above 100kHz as well as othernoisecomponents. Many therefore suggested that the supply voltage should be further smoothed by an internal linear regulator. However, others argued that this concern is exaggerated as the precision of the ATmega644 is also limited to 8 ENOB, which corresponds to 50mV at 5V reference voltage. Furthermore, all these voltage deviations occur at very high frequencies and are nicely averaged out in a typical ATmega644 measurement. Therefore the switching regulated supply should be good enough, but for precausion some kind of filtering (for example, LC filter) would be useful.However, a major disadvantage of external regulation in the case of a USB power source is thevoltage dropthrough the supply lines and the LC filter. The problem can be partially solved by reading an internal 2.5 V voltage reference when the device is switched on, which should allow to account for a voltage drop due to the average current consumption. However, the current consumption may change during the operation of the device and the resulting voltage drop could only be taken into account if the code is changed so that the reference voltage is read at each measurement.For this reason, I have opted for a compromise:The device will have both a 7-12V voltage input with a linear regulator for smoothing when very precise measurements are required, and a 5V USB input for everyday measurements.As no battery is used, all concerns about power consumption are eliminated. This simplification reduces the number of components by fourteen.As part of the optimisation of power management, the trigger button is now simply connected to the pull-up resistor and the corresponding ATMega644 pin.B.The second major optimisation can be done by simplifying the Zener test power supply, which delivers up to 5mA at 30V. I initially discarded the secondary linear regulator (Zener Test only draws about 30mA current at 5V) and the also very expensive boost converter MEA1D0515SC. Instead, I opted for the widely available and inexpensive MT3608. Normally you could use a ready-made module, but I decided to put the chip and all the necessary components on the board. This way I can access the EN pin which allows the ATmega644 to gracefully switch the Zener test power supply on and off during measurements! This reduces the number of components again by four (and possibly further two by removing LC filter).I also added an LC filter at the end of the boost up part. I'm not sure if this is really necessary as the Zener diode should keep the voltage constant regardless of the ripple and noise in the supply voltage. So there is still room for simplification.C.I have replaced two more exotic transistors BC640 and BS170 with the widely used 2N3906 and 2N3904.The first one is used to limit the current in the Zener test. As the saturation voltage for 2N3906 is slightly higher, I have adapted resistors for 1mA and 5mA.The second is used to switch on the FTR-B3 4.5 relay. The voltage drop across the transistor at 30mA is small enough so that the voltage across the relay is still above the nominal 4.5V and well above the minimum 3.38V.D.I have replaced the expensive LM4040 voltage reference with the widely available TL431. The former is generally more accurate, but the most important factor in accuracy is the grade of the voltage reference. The grade B TL431, TL431B, has only 0.5%,which is sufficient for operation with the ATmega644 and is still very inexpensive.E.The total reduction of components enables the reduction of board dimensions below 10cm. Ordering board with dimensions less than 10cm at JLCPCB is significantly cheaper.With all above optimisations the reduction in components will about eighteen and the reduction in price will be approximately $20, hopefully without signifiant reduction in precision.Below you can see the original and optimised design. Any suggestions and comments, especially the elaborated ones, are very welcome.

author: indman
author_rank: Super Contributor
timestamp: May 16, 2025, 08:15:20 am
content: You can simplify the scheme even further. Node Q6,K1,C12 is only needed if k-firmware is used. C12 can be added manually in parallel when measuring inductance. For m-firmware, it is not used at all. The protection on the SRV05-4 diode assembly and the 6V8 suppressor is ineffective, it is better to use the vacant relay K1 instead (see Karl-Heinz manual). C6 can also be removed from the circuit, the tester will work fine without it.

author: madires
author_rank: Super Contributor
timestamp: May 16, 2025, 08:55:17 am
content: I'm not sure, but I think the additional relay for the sampling ADC function isn't supported by the k-firmware yet. Please correct me if I'm wrong. To reduce the BOM I'd remove Q6, K1 and C12. Or alternatively, use K1 as input protection, as indman suggested.

author: indman
author_rank: Super Contributor
timestamp: May 16, 2025, 09:01:28 am
content: madires, I haven't repeated this particular project, so I also can't confirm about the K1 relay. I think this question can be answered by the developer of this project.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 16, 2025, 09:21:48 am
content: Quote from: indman on May 16, 2025, 08:15:20 amThank you for your comments and especially for referring me to Karl-Heinz's manual - it's pure gold with circuit explanations.It seems that DevKit-644 is actually a simplification of the circuit in Figure 2.16.I would like to add that the relay protection in Figure 2.3 is an improvement of the relay protection in Figure 2.2 on the left, while the diode protection in Figure 2.2 on the right is a different animal. Of course, I don't really understand this diode protection, so I won't comment on its effectiveness.Should I leave AREF floating or connect it to VCC?

author: indman
author_rank: Super Contributor
timestamp: May 16, 2025, 09:23:57 am
content: Quote from: Pygmalion on May 16, 2025, 09:21:48 amYou don't need to connect it anywhere, leave it empty. The new software does not need to connect this capacitor.The protection unit can be omitted from this circuit altogether. If your MCU is destined to burn up, it will still burn up no matter how sophisticated the protections are.Discharge capacitors and be careful - this is the best defense for this project!!!

author: pupkinv
author_rank: Contributor
timestamp: May 16, 2025, 11:18:21 am
content: It would be better if this project wil posted on GitGub (or else). Not need, in this case, redrow schematic here with aney changes

author: TurboTom
author_rank: Super Contributor
timestamp: May 16, 2025, 11:23:31 am
content: D4 is wrong polarity.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 16, 2025, 04:50:51 pm
content: Firstly, thank you for your comments so far.SamplingADC is mentioned in Karl-Heinz's manual. If this method is used, there is no harm in leaving this part of the circuit in place and leaving it up to the builder to decide whether to actually solder in the components.As for the benefit of diode protection, can you elaborate why it doesn't make sense? Interestingly, the SRV-05-4 has its own protection diode, but Karl-Heinz has connected P6KE6V8A in parallel, probably as a backup. This part can also be left in place and the builder can decide for himself if he wants to use it or not.There is also one point that I don't quite understand. I see that the encoder leads are connected to ATmega pins PC3 and PC4 through 1kΩ resistors, which is technically unnecessary. The only reason I can think of is that some ATmega pins are used for multiple purposes and this is a kind of protection in case the output of PC3 or PC4 is accidentally HIGH while the encoder is in operation? If so, such protection should also be used for the button line.Finally, the elephant in the room is the choice of microprocessor; I have found that the ATmega644 is quite expensive! I realise that memory might be an issue - I've seen that Karl Heinz uses assembler for k-firmare. How close is m-firmare to the limits of the ATmega328? Is it likely that the limits can actually be overcome for this design, even if it doesn't support some more complex options?

author: KungFuJosh
author_rank: Super Contributor
timestamp: May 16, 2025, 05:10:20 pm
content: ATmega644 is $7.00 here. That's only expensive if you're building in bulk.

author: madires
author_rank: Super Contributor
timestamp: May 16, 2025, 05:14:15 pm
content: Quote from: Pygmalion on May 16, 2025, 04:50:51 pmThe relay is not supported by the k-firmware yet.Quote from: Pygmalion on May 16, 2025, 04:50:51 pmSRV-05-4 is a weak input protection.Quote from: Pygmalion on May 16, 2025, 04:50:51 pmMany testers have the rotary encoder in parallel with display signal lines.Quote from: Pygmalion on May 16, 2025, 04:50:51 pmIt depends on which options you need. k-firmware automatically enables or disables some functionality based on the ATmega's flash size. m-firmware allows you to customize the firmware for your needs, and it has also some assembler code.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 16, 2025, 05:49:24 pm
content: Quote from: KungFuJosh on May 16, 2025, 05:10:20 pmHere in Europe, the ATmega644 DIP version costs €9 ($10), which isfour timeATmega328 DIP version! Even ATmega1284 is cheaper.And luckily I can buy it in a local shop, so there are no shipping costs.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 16, 2025, 05:59:58 pm
content: Quote from: madires on May 16, 2025, 05:14:15 pmI think the same applies to the PC7 pin, which means I should also put 1kΩ between the the rotary decoder button and PC7?By the way, which pin in your opinion should I reserve for future SamplingADC?Quote from: madires on May 16, 2025, 05:14:15 pmCould you say approximately how much memory the m-firmware needs for all the options available for the current design (the identification of all components plus Zener)? It seems to me that if it's all much less than 32MB, using the ATmega644 is overkill.

author: indman
author_rank: Super Contributor
timestamp: May 16, 2025, 06:04:29 pm
content: Quote from: Pygmalion on May 16, 2025, 05:59:58 pmIf you want to turn on the whole rich set of options and opportunities that M-Firmware offers today, then you don’t even have enough memory in Atmega 644. Today it is advisable to purchase a minimum of Atmega 1284/2560 tomorrow....For Atmega 328 today you have to save literally every byte of memory.

author: madires
author_rank: Super Contributor
timestamp: May 17, 2025, 09:43:30 am
content: Quote from: Pygmalion on May 16, 2025, 05:59:58 pmAny unused IO pin but ADC_PORT and R_PORT. Staying away from pins used for hardware SPI, I2C and serial is also recommended (ATmega644 or better).Quote from: Pygmalion on May 16, 2025, 05:59:58 pmThe basic fuctionality for detecting components and the Zener check fit into 32 kB. The best would be if you enable the features you want, compile the firmware, and see how much flash it needs. Displays have also an impact on the firmware size.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 17, 2025, 08:47:56 pm
content: I was playing PCB Tetris today and here is my amateur design for the board of the proposed circuit:I didn't leave anything out, I might even fit a thing or two on this 10x6.5 board.I don't understand why so much space is needed for the protection diode? Also, the voltage divider for the Zener test is in a completely different place than the Zener power supply - I didn't change the position because I didn't know the reason.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 17, 2025, 09:08:57 pm
content: Quote from: madires on May 17, 2025, 09:43:30 amYes, I'm slowly grasping your design. Apart from the measuring pinsgeneral probes (PA0-PA2, PD2-PD7)Zener probe (PA3)adjustment capacitor (PA7 and PC5)there are a few pins that cannot be sharedreference voltage (PA4)trigger button (PC7)power control (PC6)sampling ADC(PC2)battery check (PA5)Zener control (PC2)Now I understand why you trigger the Zener test with a button: you wanted to save one pin. I could do that too, but then I would need another transistor and two resistors to reverse the logic. But what the heck, I don't need the battery check and the power supply control anyway, so I chose PC6.Quote from: madires on May 17, 2025, 09:43:30 amGulp, I am too much invested in this design to go back to the ATmega328. Maybe I can add an IR decoder or logic control to use the excess memory in the chip and the excess space on the board.I invite everyone to vote on what else you would like to see on this board!

author: Per Hansson
author_rank: Unknown
timestamp: May 18, 2025, 05:39:02 am
content: Quote from: Pygmalion on May 17, 2025, 09:08:57 pmThe option to start the Zener test via a pin was added to the software after Madires had already made that Devkit hardware design....Quote from: Pygmalion on May 17, 2025, 09:08:57 pmIt is a good thing: if you used a 32KB Atmega you would forever be annoyed by that choice later.I run k-firmware on one tester with Atmega 328 and even that I have to really carefully play with and choose what to leave out to remain within the memory limit.Then for m-firmware an Atmega644 is used and it is so much less annoying to compile forQuote from: Pygmalion on May 17, 2025, 09:08:57 pmReplace the current SRV-05-4 protection diode that is pretty useless with the relay based protection.And make it more clear that the protection and zener test components are optional on the PCB if you want to save cost, it makes a big difference.

author: madires
author_rank: Super Contributor
timestamp: May 18, 2025, 11:05:34 am
content: Quote from: Pygmalion on May 17, 2025, 09:08:57 pmThe ADC input for the external 2.5V reference can be shared with the protection relay. This was done because of the lack of unused pins for the ATmega328 based design. And we keep it for compatibility reasons.Quote from: Pygmalion on May 17, 2025, 09:08:57 pmYes, same story as above. If you want to keep it compatible with the k-firmware stay with the test button. Running the boost converter all the time (when the tester is powered on) might possibly work too with the k-firmware (not tested yet).

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 18, 2025, 02:59:19 pm
content: OK, thanks for the feedback so far. I would like to find some information.My idea is to build a device that complements the devices that a typical hobbyist like me already owns, for example a good multimeter. A typical multimeter today not only measures resistance, current and voltage, but often also capacitance, diode forward voltage and frequency.So what I'm really missing at the moment is measuring ESR resistance, inductance, zener diode voltage and most importantly recognising the properties of different semiconductors. From what I've read so far, 32kB should be more than enough for all that.However, if I decide to add another option in the future, this could be a problem. If it's a software option, it's not a problem, I'll recompile the firmware. But if it is a hardware option, I will have to build a new Transistor Tester.What do you think is the most likely hardware option that I might miss in the future so that I can fit it on the free space on my board?As for protection, the relay protection protects the tester when it's not measuring, if I understand correctly. But what's the point - if you're not measuring, nothing gets plugged into the probes? I'd really like to understand that, because as I see it, diode protection, ineffective as it may be, still makes more sense. Of course, changing the protection is a small thing and only requires redesigning a very small part of the PCB. At the end of the design process, I can easily make both relay and diode protection variants, so everyone can choose the one they like better.madiresIs there a reason why you put the voltage divider of the Zener test on the completely opposite side of the board?Is there a reason why you placed the protection diode the way you did? According to the datasheet, the protection diode has a tiny DO-15 package and has no special mounting requirements, whereas you use a large P600 package and mount it vertically.

author: madires
author_rank: Super Contributor
timestamp: May 18, 2025, 04:23:40 pm
content: Quote from: Pygmalion on May 18, 2025, 02:59:19 pmI can't answer that because I have no idea which hardware options you might need in the future.Quote from: Pygmalion on May 18, 2025, 02:59:19 pmThe protection relay shorts the probes when the tester isn't running the probing cycle.Quote from: Pygmalion on May 18, 2025, 02:59:19 pmIt simplifies the layout in that particular case.Quote from: Pygmalion on May 18, 2025, 02:59:19 pmThere are also TVS diodes with DO201 or CB417 packages (1.5KE or P6KE series).You don't have to follow my circuit, BOM or layout. The DevKit-644 was designed as development platform, to be compatible with k and m-firmware, to support connecting any new hardware options or displays, and to allow DIY-ing the PCB It's not meant to be a polished product.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 19, 2025, 08:28:25 pm
content: First I would like to say that sometimes when I don't understand the reason for a particular solution, I assume that there is a good reason for it that I just don't understand. That's the reason why I sometimes ask these annoying questions.I have redesigned the circuit part around the button so that the zener test can be controlled by either the button or the microprocessor, with the microprocessor trumping the button. It's essentially a NOT gate with a resistor in the direction of the microprocessor's PIN. It was quite difficult to optimise the resistors - I even had to use LTspice.Once I added that to the board, I was able to complete the optimisation and still have some space on the board. I took a look at the m-firmare manual, and the LC meter and ring tester look interesting, but no circuits are included. Where can I get them? What about the optocoupler tool, does that require additional hardware?Below are the pictures of the current state of the schematic and board. If anyone is interested, I can also provide KiCAD files - maybe I should add this as a project on github.

author: madires
author_rank: Super Contributor
timestamp: May 20, 2025, 10:01:16 am
content: Please see the repohttps://github.com/madires/Transistortester-Warehouse/tree/master/Hardwarefor the hardware options not noted in Karl-Heinz' documentation.

author: indman
author_rank: Super Contributor
timestamp: May 20, 2025, 12:22:31 pm
content: Quote from: Pygmalion on May 19, 2025, 08:28:25 pmYou still have a lot of work to do on this project, but you don't listen to the advice you are given.What kind of display are you going to connect to the board? If large and color, then a level converter must be added to use hardware SPI. It is also common for the display to be placed on the board in advance, so that it can be quickly and easily connected to the top of the board. This makes for a compact design.

author: ledtester
author_rank: Super Contributor
timestamp: May 20, 2025, 02:12:13 pm
content: Quote from: Pygmalion on May 19, 2025, 08:28:25 pmWhy did you make R17 so large at 270K?

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 20, 2025, 06:05:29 pm
content: Quote from: indman on May 20, 2025, 12:22:31 pmThanks for the warning, but don't worry about the display. I have a dozen different displays that I've written and published some code for on the Raspberry Pi. The idea is that my device is modular, so I can just connect one of the displays with cables later.

author: indman
author_rank: Super Contributor
timestamp: May 20, 2025, 06:09:54 pm
content: Quote from: Pygmalion on May 20, 2025, 06:05:29 pmWhy connect the display with a cable, if you can immediately connect it to the connector on the same board?

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 20, 2025, 06:11:20 pm
content: Quote from: ledtester on May 20, 2025, 02:12:13 pmR17 must be much larger than R18 in order to get close to 5V on Button line when button is not pressed.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 20, 2025, 06:17:08 pm
content: Quote from: indman on May 20, 2025, 06:09:54 pmIf someone makes such a request, I can do so.Personally, I want to have the freedom to test and use different displays. If I am eventually happy with the final result, I will print the box and attach the display to the top of the box. I have already done that with other projects.

author: indman
author_rank: Super Contributor
timestamp: May 20, 2025, 06:24:55 pm
content: Quote from: Pygmalion on May 20, 2025, 06:17:08 pmYou did not quite understand my thought. You placed a universal connector on the board for connecting various displays. This is normal. But you have a lot of space on the board and there will be even more if you remove the extra details that I wrote about before. Thus, there will be enough space on the board to install a level converter and place a nesting connector for a quick connection of the most commonly used ILI9341/ST7789 displays with a screen of 2.4-2.8 inches.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 21, 2025, 09:41:07 am
content: Quote from: indman on May 20, 2025, 06:24:55 pmAs far as I remember, you suggested removing the diode protection, which doesn't actually take up much space and is on the wrong side of the board.Initially I will just use 5V ST7920 which I already have on hand. But let's assume that later I decide to buy and use a different 3.3V display. Which lines do you think should be accessible via the level shifter? I assume that only 5V -> 3.3V should be required, as displays only receive commands.

author: indman
author_rank: Super Contributor
timestamp: May 21, 2025, 09:56:36 am
content: Quote from: Pygmalion on May 21, 2025, 09:41:07 amIf you are not using a relay as a protection instead of a diode assembly, then this relay can also be removed from the board.It is not needed and is unlikely to be needed in the future. C5 is also not needed, I have already written to you about this.Quote from: Pygmalion on May 21, 2025, 09:41:07 amIt is unwise to use a black and white display for this ATmega644-based project. The color display is much more convenient in terms of comfortable reading of information. See themadiresdocumentation for which signal lines are needed to connect the ILI9341 hardware SPI interface or an 8-bit parallel bus.

author: madires
author_rank: Super Contributor
timestamp: May 21, 2025, 11:39:16 am
content: I'd stay away from the ST7920 anyway, it's a terrible LCD controller.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 21, 2025, 04:19:28 pm
content: Would ST7920 be good at least for testing, because I already have one at hand?So you would propose that in a long run I should use either ILI9341 or ST7789 and prepare also logic shifter for the required lines?

author: indman
author_rank: Super Contributor
timestamp: May 21, 2025, 05:00:07 pm
content: Quote from: Pygmalion on May 21, 2025, 04:19:28 pmFor testing, any display that is supported by authors software is suitable.Quote from: Pygmalion on May 21, 2025, 04:19:28 pmIf you do this project only for yourself, then you can leave as you designed earlier. But if you want other people to be repeated, you should think about what I suggested.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 27, 2025, 08:01:57 am
content: Quote from: indman on May 20, 2025, 06:24:55 pmI'm reading config_644.h and didn't find anything on ST7789, so I don't know how to prepare for this display chip. On the other hand, I found this on ILI9341:#define LCD_RES PB2 /* port pin used for /RESX (optional) */#define LCD_CS PB4 /* port pin used for /CSX (optional) */#define LCD_DC PB3 /* port pin used for D/CX */#define LCD_SCL PB7 /* port pin used for SCL */#define LCD_SDA PB5 /* port pin used for SDA/SDIO */Since PB3, PB5 and PB7 are not used for other functions, I guess chip select is really not necessary. So only PB3, PB5 and PB7 should be shifted to 3.3V and a 3.3V power supply line should also be present.It is also questionable whether I can provide direct pin socket as the pinout of displays changes.Can you confirm that my thinking is correct?

author: indman
author_rank: Super Contributor
timestamp: May 27, 2025, 08:52:05 am
content: Quote from: Pygmalion on May 27, 2025, 08:01:57 amST7789 is completely compatible by the interface with ILI9341 (only the image orientation can differ) and this is tested in practice.Madireswill have this addition in the new version.Quote from: Pygmalion on May 27, 2025, 08:01:57 amYou need to get more information about how the hardware interface works. It's not enough for you to just match the 5V and 3.3V levels.It is very desirable to install a fast converter, otherwise large color displays will simply not be able to operate fully on these data buses.

author: Pygmalion
author_rank: Regular Contributor
timestamp: May 27, 2025, 01:48:03 pm
content: Quote from: indman on May 27, 2025, 08:52:05 amWhat is a fast converter?As far as I understand it, you need five connections for the ILI9341/ST7789: 3.3 V, ground, MOSI, SCK and DATA/COMMAND lines, the last three for the 3.3 V logic.So it is essentially another 3.3V linear regulator with two capacitors and CD4050B converter.

author: madires
author_rank: Super Contributor
timestamp: May 27, 2025, 02:00:41 pm
content: A 74HC4050 works fine as level shifter for a 16 MHz ATmega, hardware SPI and ILI9341/ILI9342.

author: indman
author_rank: Super Contributor
timestamp: May 27, 2025, 02:15:40 pm
content: Yes, preferably a 74HC4050 rather than a CD4050. CD4050s are very often fake and don't work well in a circuit.

author: Pygmalion
author_rank: Regular Contributor
timestamp: June 02, 2025, 07:58:05 pm
content: Well, you obviously do not approve my 2 AA powered design. So I went back to the original design and I think it's almost done.This design has essentially the same features as DevKit-644, withpower by either by USB or >7V power supply,optional MCU-controlled Zener power supply,3.3V power supply, DC, SCL and SDA lines for the display (indman suggestion)dimensions only 10cm x 6.5cmInstead of the 4050 chip, I simply used three voltage dividers; they have a slightly larger footprint but are much more flexible so I could squeeze them into the top right corner.The power section is drawn in single section because different power parts share common capacitors (5V and 3.3V regulators share C10 at the input, MCP1702-500 output, MT3608 input and USB input filter share C12).Note that I designed the power section so that the 3.3V line is not supplied by the 5V line, but directly from the outside. Therefore I had to add the diode D8.And I still have some room on the board, but there's no hardware option small enough to be put there. I was actually considering replacing the protection part with a ZIF socket, but I think those ZIF sockets are ugly. Is there really an argument in favour of using them?One remaining question is which would be the best GPIO choices for the Zener power control and ADC sampling? I've been using PC6 and PC2, respectively, but if it would be better to use a different one for compatibility reasons, I can make a change.I would also like to add a test pad for SMD components, but I don't know which component/footprint to use in KiCAD. Any suggestions please?Other than above mentioned details, I think this can be considered a final design unless you find an error or give other suggestions. THANKS!

author: Messtechniker
author_rank: Frequent Contributor
timestamp: June 04, 2025, 09:28:08 pm
content: As far as I know, the firmware does support serial communication.....

author: Pygmalion
author_rank: Regular Contributor
timestamp: June 05, 2025, 06:32:23 am
content: Quote from: Messtechniker on June 04, 2025, 09:28:08 pmThanks for the feedback. I just followed DevKit-644's example. Luckily it doesn't take up much space, so it can stay.Does the rest of the circuit seem reasonable to you?

author: Per Hansson
author_rank: Unknown
timestamp: June 06, 2025, 07:46:03 am
content: I'm gonna sound like a broken record but I'll just say at again with this quoteQuote from: Per Hansson on May 18, 2025, 05:39:02 am

author: spanakop
author_rank: Contributor
timestamp: June 06, 2025, 09:06:08 am
content: Hi guys, I don't want to hijack this thread, but trying to follow this discussion with people referencing images I can't see is difficult.Is there any setting that turns the post images on/off, because I can't see any in this thread. In other threads I can see images fine.I'm using Firefox as my default browser, I also tried a Chrome based browser, both had the same issue. If I look at this thread via my phone (again with Firefox), I can see the images. I have tried this logged in and logged out with no difference.

author: Per Hansson
author_rank: Unknown
timestamp: June 06, 2025, 09:49:22 am
content: The images are hosted on this website:https://i.ibb.co/tMtpZs0b/tester1-pcb.pngMaybe you have an adblocker or HOSTS file entry that blocks access to that website?

author: spanakop
author_rank: Contributor
timestamp: June 06, 2025, 09:53:59 am
content: I disabled any add blockers when testing earlier.Ah, i've found the problem. I'm viewing this on a company laptop, and that site is blocked because it's classed as a file share site.Thanks for help. Case closed.

author: Pygmalion
author_rank: Regular Contributor
timestamp: June 06, 2025, 03:25:01 pm
content: Quote from: Per Hansson on June 06, 2025, 07:46:03 amNo problem. I have taken note of that. The protection is there for legacy reasons, since DevKit-644 has it. Of course, I'll probably end up making two versions, a legacy one with the protection and a new one with the protection replaced by either a ZIF socket or something like that:The green ones are available in 2.54 and 5.08 pitch, and both take up much less space as they exist in the three-contact version (while the ZIF socket has 11 contacts in excess).