C64 Cynthcart Controller

DIY STUFF
21

You can power it with 5 V no problem, and the circuit isn’t using a lot of power so using the C64 supply should be ok.

However, note that the Arduino power is misconfigured; you should supply +5V to pin 27 (+5V), not pin 30 (VIN). See here:

Using 100k instead of 10k may cause problems, though; the analog inputs on the Arduino have a sample and hold circuit with a small capacitor, and they recommend that the circuit driving the input has an impedance <10k. See here:

EDIT: To clarify, the maximum output impedance of a potentiometer divider is R/4 (half the resistance in parallel with the other half), so a 20k potentiometer would be ok, but 100k is pushing it.

22

Oh wow thank you very much!

1 Like
25
3 Likes
26

I decided to embark on my own C64 synth project. Started documenting it here, beginning with Cynthcart:

4 Likes
27

I built this a while ago with LMNC’s PCBs and it was working great! But now most of the controls don’t work anymore. Some knobs send midi messages fine others don’t seem to be sending any info to the arduino and no midi messages come out from the device.

Ive tried debugging it but i’m stuck now, this is what I’ve tried

  • checking the pots resistance changes when you turn them with a multimeter
  • trying a different CD74HC4067 chip
  • checking the connections for all the pots to ground and to the CD74HC4067
  • re-uploading the code to the arduino
  • checking the midi out with MIDI Monitor via a Roland UM-One USB adapter
  • powering it by the 9v connection as well as from the arduino USB

Usually 4 of the controls work fine Tremelo D, Env R, Filter Q, and Modes Mod. Sometimes other controls work but it is intermittent which is weird.

If anybody has any other ideas on what else I can debug i’d really appreciate it!

28

Turns out that some of the pots had a short? between the ground and signal pins, pulled them all out and ordered different ones

image
image1920×2560 430 KB

29

Where did you get your CD74HC4067 chip? I can only find those mini breakout board things.

I’ve found CD74HC4067E chips available. They look to be similar. Any ideas if they can be swapped out for these? I’m not an IC expert by any stretch :smiley:

Edit: looks like the schematic says CD74HC4067M but the video @lookmumnocomputer put together uses a CD74HC4067E, so I’m going to grab the latter and try that!

1 Like
30

In general, suffixes on ICs indicate different packaging or grade (temperature range or voltage range or perhaps speed) or how it’s delivered (on a reel vs taped vs in a box or whatever). If you want to know what each one is, take a look in the datasheet - for example from here:

You can see this bit:
image

Here - the E suffix denotes that it’s a DIP package - what we like for doing DIY stuff. Other packages are small surface mount and harder to deal with for hobbyists - although it’s not impossible.

Some of the older CD4000 series logic have things like B and U suffixes which can mean buffered or unbuffered. Sometimes, in synth circuits where people are using the logic chips “creatively” the differences between B or U part can be important.

Generally, I like to try and understand what each part of the part number is telling me, so that I can then make judgement about what can or can’t be substituted in a particular design.

Cheers

5 Likes
31

Thanks! I think what threw me was that both the Gerber and schematic list the chip as CD74HC4067M, but the DIP version is E, so I wasn’t sure if I was missing something there. :slight_smile:

1 Like
32

CD74HC4067E is no longer manufactured. :frowning_face:
I ordered few chips from Aliexpress but they are all crap. I ordered CD74HC4067M from dig-key but this chip is way too small to fit on the PCB.
Does anyone know what I can use as replacement? Or where I can buy them?

Thanks

33

A bit on the spendy side but maybe this will do the trick?

1 Like
34

I’m not sure it will fit perfectly on the PCB but I will definitively give it a try.
Thanks Jaradical

35

Doesn’t fit but your could possibly make an adapter in stripboard? I found my CD74HC4067E on eBay but I’m having trouble with my build and this could be the issue?

36

I found another alternative for the CD74HC4067E. I think we can use CD74HC4067M + an adaptor

1 Like
37

Woof these have gone up in price. No surprise all things considered, but I bought one about a year ago for I think half of that.

38

Aside from being expensive you need to take care with the pinout when using this kind of thing. I learnt the hard way that DIP and SOIC footprint for the same device aren’t necessarily always the same…

3 Likes
39

Good point. I will read the specs before installing it and let you know if it works.
Thanks Jared.

1 Like
40

Hey, how you doing, I realize that was almost a year and a half ago, but you wouldn’t happen to still have any extra Cynthcart controller boards you’d be willing to part with, would you? Just figured I’d ask before I order a whole batch. Thank either way!

1 Like
41

Oh hey, sorry for the delayed reply. I might actually still have one. Whereabouts in the world are you? Sling me a DM!

2 Likes
42

Hi,
Has anyone managed to build one using Sam’s PCB? I am blocked. The code and the circuit seems to be ok but I don’t have MIDI signal from the MIDI OUT.
Could someone post a image of the back panel of its Cyntcart controller (in good resolution)? I think that would help me to verify if all my connections are ok.

Thank you.