Eurorack module testing tool (DIY)


Update found it :slight_smile: 64W-20K

do you have the reference number from reichelt for 20k trimmer ?


So, after getting the voltages above lined up perfectly (1V and super close to 3V), I used the Eurorack Module testing tool to tune a bunch of VCO’s and it is amazing how well it works! I was actually surprised at how far off a couple were.


What calibration strategy did you use?
I find it best to adjust the offset to get 3 V volt first, then adjust the scale to get 1V. Then repeat.


Thats exactly what I ended up doing. I repeated a few times.


Hi All, I have poor knowledge of Atmel MCU’s. When I try to do the fuse bit’s in Atmel Studio it pops up a message saying the value of the EFUSE 0xFD will disable the JTAG. Won’t this cause a case of the code not being able to be flashed? The problem with my tester is all the lights are on and while the display shows the correct items the response is slow and erratic, so I’m trying to reflash it. The Atmel chip was bought pre-flashed.


Looks like I got it working. I took the plunge and just copied the fuse and flash lines of code a few pages back with avrdude and all good. Lights etc behaving as expected. Thanks to all posters and Oliver.


As an explanation for your JTAG error message:

On AVRs that have both JTAG and ISP, you can safely disable one of the two. You’ll usually use ISP and JTAG is only useful for debugging. Many projects need the JTAG pins for other stuff and then JTAG has to be disabled so that the pins are free for their intended use. Apparently Atmel Studio warns you about that. AFAIK avrdude doesn’t warn you on this.


i inherited a faulty unit in a trade and its having very similar issues to a previous poster ‘gerard’(so much so it might be the same unit!) ive tried PMing him but no reply.

the screen is all blocked out and unreadable and changes with turning the encoder and it generates a tone when plugged in the audio out. so that means the chip is ok?? or should i look into reflashing it?

ive re-flowed the whole board but still nothing.


Can you describe what the display is showing? One line all black, and one line all white?


as attached, from earlier posts, not my own.

although when you turn the encoder thehe distribution of the squares is sometimes all on the right hand side of the screen,top and bottom rows. like this -

sorry im not near the unit right now to take actual pics but these illustrate it close enough.

Also the LEDs above the buttons are not lit at all, ive tried bridging the legs with another led to see if the polarity was wrong but no luck.


Well, the orange display looks like an uninitialized one. The red one- I don’t know whats going on there…


ive replaced the display and it works! thanks for everyones help.

I cannot figure out the calibration process though- i have it set to the cv out settings on the main project page and plugged a lead into the cv out , using my meter ive attacehd teh COM lead to the shaft of the jack and the + lead to the tip.

im getting 10.6v with no apparent change to the value when i turn the trimmers. im doing somethign fundamentally wrong, arent i?


It’s probably another assembly mistake… 10.6V looks like the voltage of a TL07x clipping (due to a missing feedback resistor or excessive gain, or maybe the V+ input being not grounded).

Check everything around IC2C.


it looks alright, see pics, also just to be sure- is the adapter correct?

btw power out of the module power cable is 11.36v

other functions eg clock rate, audio out seem to be working


Looks like a DC adapter - you need one that provides AC (12V if I recall correctly).


Indeed, wrong adapter, so all the analog section of the module tester is missing its negative supply…


jolly good! i feel a mixture of happiness and shame. i hope not to report back with more problems when i have the correct PSU.


all working thanks for all the help and for the excellent gadget olivier


Is 500mA (12V AC) sufficient to power the module tester. Couldn’t see the Amps for the PSU specified anywhere so sorry if this is a duplication…


Depends a bit on the modules you’ll be testing, as these will be powered from the tester …