Help with "Semi modular" DIY Drum Machine

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Monkeproggs
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Help with "Semi modular" DIY Drum Machine

Post by Monkeproggs » Mon Jul 27, 2020 2:32 am

So I've got a crazy idea to build a drum machine. I've started breadboarding separate pieces and found them to work but I can't breadboard the whole thing. I must have tried at least 25 differnt setups for sounds before deciding on these.
So I thought maybe I can get some pointers from some experts.

The setup is quite simple:
I've got a NE555 as clock (with obvious Clock in coming, it's not on the shematic yet) driving a CD4017.
This 4017 I want to sent to a matrix of 8x4 patchpoints. Every step is sent to a row of 4 outputs.
Output1>---XXXX
Output2>---XXXX
et cetera et cetera Like so:
Drummaschine Matrix_schem.png
These outputs are then patched into another matrix where the signal is sent to the various sounds of the drummachine.

XXXXXXXX---> SNARE
XXXXXXXX--->Bass Drum
XXXXXXXX--->High Hat
XXXXXXXX--->Woodblock
Like so

So in effect you can "program" it by connecting cables to each step and the corresponding sound. If you'd like you can play all sounds all the time.
Will also be adding a Clock divider so you can get sounds to play every 2,4,6,8th time it's triggered.
This is my intention.

I Have a basic layout that I'm working on, and would like som input on the circuit.
A few questions have come up:
Do I need to "buffer" the output from each step if I'm going to send it to multiple inputs? and how?
Do I need to put a Diode on every input?
Do i need to put a diod on every output (in the matrix)?
Will it work?

Thankful for any pointers given and any correction. I'm more of an enthusiast than electrician so my knowledge has limits.
Posting a schematic for it too (it's big).
Drummachine_schem.png
Thank you
/
Monkeproggs
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JimY
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Re: Help with "Semi modular" DIY Drum Machine

Post by JimY » Mon Jul 27, 2020 4:02 am

Nice project.
Could you perhaps zoom in on the sequencer part - the resolution of that image is too low to zoom in and read!
Only 4 tracks, so I personally would get a quad AND gate to use as buffers and add the possibility of clock gating.

Will it work? I'd have to see the sequencer in detail. It looks like your hoping to use the 4017 steps as triggers. But you probably need to sequence a trigger-gate arrangement...
Reset. Q0 is active.
Start - first clock triggers active instrument.
Increment 4017 to next step
Trigger next step
...and so on until resets back to Q0
So the sequencer is sequenced! It's asking for trouble to try and step and trigger at the same instant in time.
4017 can drive LED's directly (handy that only one can be lit) - but use high-efficiency LED's and make the common resistor value as high as you can and still see the lights well.

Monkeproggs
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Re: Help with "Semi modular" DIY Drum Machine

Post by Monkeproggs » Mon Jul 27, 2020 10:40 am

The sequencer works that i have tried a lot of times (and built) Im curious if it actually will work to sent the trig to all differnt sounds. I've breadboarded the bassdrum and the noice part, but not all at the same time.
Drummachine_schem.pdf
Drummaschine Matrix_schem.pdf
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Re: Help with "Semi modular" DIY Drum Machine

Post by Monkeproggs » Wed Jul 29, 2020 3:21 am

Drummachine2_schem part.jpg
I redid, the sequencer part as per instructed on various boards and added a clock in option and a reset for the sequencer. I will put an start/stop-Step function later.

I would really like it if someone took a look at all the opamps in the schematic, as I'm quite new to working with them and am prone to making rookie misstakes therefore.

Thank you great wizards of Ohmmmmmmmmmmmmmm
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Whelm
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Re: Help with "Semi modular" DIY Drum Machine

Post by Whelm » Wed Jul 29, 2020 9:03 pm

I'm building something very similar right now, but with an Electric Druid TapLFO chip clocking the CD4017 instead of a 555 and it's not modular. I barely have any idea what I'm doing so I can't offer advice but we're in the same boat.

I plagiarized the LED section from the MFOS 10-step sequencer using transistors to drive the LEDs. Not sure if that would offer an advantage over driving them directly off the 4017.

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JimY
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Re: Help with "Semi modular" DIY Drum Machine

Post by JimY » Thu Jul 30, 2020 8:42 am

Are you sure that sequencing is still right? Won't it advance to step2 the moment the first clock pulse happens? This might appear to work, and you might get a trigger off step 1 because the 4017 logic has a short delay from the clock pin going high to changing the count outputs, but it will be immediately followed by a trigger from step2 .
If you use the spare 74HC14 inverter and put it between the clock and the 4017 clock input pin, then the first clock High going pulse after start will trigger step 1 but not advance until the clock pulse falls low when the inverted clock will advance the counter ready for the next trigger. Alternatively, you can feed the clock to pin13 and tie pin14 to +9v and that will invert the 4017 clock without an extra part.

You've probably simplified the drawing, but you do need a complete set of x8 blocking diodes from the step outputs for each instrument track otherwise you can't connect steps for one without affecting the others. The logic gates will be quite capable of driving them all.

The opamps seem ok to me without knowing the circuits all that well, but the unused opamp should be terminated or else it can cause random interference. Simply connect pins1 & 2 together and pin 3 to the joint between R4 and R5.

If you don't use the spare 74HC14 inverter, you should tie its input to 0v or +9v to keep it stable.

If you know the trigger inputs will always be connected from the step diodes, you don't need the blocking diode in the trigger input - but it won't do any harm keeping them.

The MFOS design probably dates from when most LED's were the old 20mA type, and they needed more current to light brightly. Modern LED types are more efficient, so you can get away with driving them direcly from logic in most cases - but you do need to a fit a higher value resistor in series with the LED or you don't gain from the improved efficiency - and get blinded. Note that many LED resistor guides that you find are still for the old 20mA LEDs.

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Re: Help with "Semi modular" DIY Drum Machine

Post by Monkeproggs » Thu Jul 30, 2020 5:13 pm

I think the sequencer is done right. It works on my breadboard. And yes the 4017 is abit wonky but I wanted to do this with what i had and as many passive components as possible. I will of course double check before I actually make this into a pcb.
Blocking diodes
are they different from the diodes I have on each step from the 4017 as well as on each input in rhe matrix?
If so please attach a quick drawing to explain. As I mentioned Im a beginner with doing correct electronics as opposed to just trial by error...
Thanks for all the input regarding terminating unused parts of the ICs.
Had initially planned on using 5 different sounds but due to laziness i decided that the matrix was enough with 4x8 pinports times 2.

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JimY
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Re: Help with "Semi modular" DIY Drum Machine

Post by JimY » Sat Aug 01, 2020 4:18 pm

I have suggested two ways of fixing the sequencer without adding anything else! You need to realize the 4017 counter doesn't have an output state where all outputs are Low (unlike a binary counter). When reset, the first step Q0 is already set high. If you have LED's connected to the 4017 outputs, step 1 LED will be lit to prove this. So the moment you start the clock, it advances the 4017 count to step 2 and will trigger sounds on that step. I'd think you'd want the sounds selected on step 1 to sound first, not step 2?

I meant the diodes you have on each step output from the sequencer. They are needed to separate those outputs from interfering with each other when more than one step is connected to an instrument track. So if you set up an 8beat of X000X000 for the kickdrum, the 1st and 5th counts will be joined together to trigger that instrument. The diodes block the selected step High voltage level from being pulled Low by the other outputs that are Low (in my example beat, when step 1 is High, step 5 is Low). The diodes "block" this interference. For the same reason, each instrument track needs its own set of these blocking diodes or else you will be joining all the instrument triggers together. So each output from the AND gates will be connected to x4 diode anodes. Yes, 32 diodes! I think that is easier to explain in text than to draw!
You're not being lazy limiting to 4x8. You're being sane.

Myself, I'd use 2 rows of 8 centre-off toggle switches. It would mean only having 2 instruments that can trigger on any step - each switch in a row sets sound A or B or nothing, but also only needs 2x8 blocking diodes needed for 4 instrument tracks.

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Re: Help with "Semi modular" DIY Drum Machine

Post by Monkeproggs » Mon Aug 03, 2020 3:50 am

Yes I see well it doesnt really matter if you have to start the sequencer first and let it play through a cycle, Right now I'm more focused on it actually working, however I will put a start stop function with a reset so it will help abit.
If you use the spare 74HC14 inverter and put it between the clock and the 4017 clock input pin, then the first clock High going pulse after start will trigger step 1 but not advance until the clock pulse falls low when the inverted clock will advance the counter ready for the next trigger. Alternatively, you can feed the clock to pin13 and tie pin14 to +9v and that will invert the 4017 clock without an extra part.
I will definately try this though as it seems like an elegant solution. Thanks.

I think I will need to buy a bigger breadboard to properly test this all in all. Just have to break a leg so I have the time to start. :-)
So far just trying to untangle the design for the PCB is driving me mad, there are sooo many connections it's almost impossible to get it right.

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JimY
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Re: Help with "Semi modular" DIY Drum Machine

Post by JimY » Mon Aug 03, 2020 8:07 am

I think there is a limit to how much a person can have breadboards and keep control of it all. I would suggest splitting it into known working sections and soldering them up on vero or perfboard as you prefer. If you fit 0.1" pin headers on the boards, you can use breadboarding pre-wired jumpers (the kind Arduino developers use) to connect together. Leave room in the boards for any modification (I find perfboard easier to mod). In can be a mess to assemble into a case with all the different bits, but at least you can get there... and if you make, say, a snare board, you'll always have a working snare.

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dot matrix madness
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Re: Help with "Semi modular" DIY Drum Machine

Post by dot matrix madness » Mon Aug 03, 2020 8:44 am

Splitting the whole circuit into functional sub-boards (sequencer, individual drums) will also make the project more interesting
for those who already have their favorite drum modules and are looking for (another) nice sequencer.
Licenced to solder since 1993

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JimY
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Re: Help with "Semi modular" DIY Drum Machine

Post by JimY » Mon Aug 03, 2020 11:33 am

Just checking some of my old designs using 4017 and I actually made the same mistake with clock/step timing - but I got away with it because the clock circuit I used always started at high level so the 4017 didn't step straight to Q1. It has to see a clock transition from low to high to step. I'm not sure what the 555 based generator will do.

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