How can I double a schematic when making my own module?

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groffcole
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How can I double a schematic when making my own module?

Post by groffcole » Tue Jun 09, 2020 1:19 pm

I'm learning and getting into the synth diy stuff. I'm going to build a eurorack system and I've got a handful of nice prototyping boards.

I'm trying to think of how I can double a schematic so that I have a double module - for example, a double adsr envelope generator. If you take the schematic on this page: https://www.yusynth.net/Modular/EN/ADSR ... atest.html, would I need to change any component values if I were to double the schematic in the same module? What if I wanted to squeeze four envelope generators onto my own prototyping board?

From my brief reading in a beginner's electronics book, I am thinking that I can plop two circuits onto the same board and the only difference would be that the entire "double module" would consume more amperage. Something like that.

I hope this question makes sense.

Thanks!

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emmaker
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Re: How can I double a schematic when making my own module?

Post by emmaker » Tue Jun 09, 2020 3:40 pm

As for circuit values probably not. If you are putting multiple units on a single board you would want to share a common power connector. Depending on the circuit things might change there or not. Really depends on the circuit and how you wire it up.

When you duplicate the circuit in the PCB program you will need to change the component designators though. When you cut and paste part of a schematic in some software it will generate new designators.

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EATyourGUITAR
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Re: How can I double a schematic when making my own module?

Post by EATyourGUITAR » Wed Jun 10, 2020 7:58 am

the hard part is mixing digital signals and analog signals from two different circuits. there are many books on network analysis and PCB design. the many small differences in how people handle power distribution and protection on any module design are too numerous to list here. if you expect crosstalk or power problems between the two circuits, you may have to design in some way of increasing power supply ripple rejection on each sub circuit because they do share one power connector. this will come later. you should avoid trying to learn the hard stuff before building your first module. go ahead and build it. test it. there is time to read books later if you think you like it.
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fitzgreyve
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Re: How can I double a schematic when making my own module?

Post by fitzgreyve » Fri Jun 12, 2020 3:46 am

There are two things to consider here:

1. Will it work? - For something like this (no heavy power consumption, no high speed digital signals) there should not be a problem. There is minimal difference between duplicating the circuit on one pcb, and connecting together several PCBs each containing a single circuit. I would keep it simple and design the PCB so that each ADSR circuit was separate from the others (physically and electrically), with the power (including 0v) for each ADSR going direct to the single power connector on the PCB (aka "star" arrangement).

2. How to actually design it: In essence you are going to want to enter the design once into your design software, then "cut and paste" it:

2A. In some simple PCB design software (my experience is the earlier versions of ExpressPCB) you can do the schematic for one ADSR, design the PCB layout for it, then cut and paste (duplicate) just the PCB layout, finally join up the power connections. In this case you will have multiple R1, multiple U1 etc. The PCB software may throw out warnings about this, but they can generally be suppresed.

2B.In other design packages (I use RS DesignSpark PCB) you will need to duplicate the ADSR in the schematic, then transfer the whole thing to the PCB design. Each component will need it's own unique reference number: I would make ADSR1 1xx, ADSR2 2xx etc: R101 = R201, IC101 = IC201

I hope this is clear.
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groffcole
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Re: How can I double a schematic when making my own module?

Post by groffcole » Mon Jun 15, 2020 10:38 am

Thanks for the advise, everybody. It sounds like I just need to be patient and keep learning some new things. But this puts me in a good place to start researching.

I don't think I'll be using any circuit design software, but rather I'll probably be using a breadboard-like prototype pcb.

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J3RK
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Re: How can I double a schematic when making my own module?

Post by J3RK » Mon Jun 15, 2020 11:00 am

As mentioned above, if you're using a software package that handles the netlist between the schematic portion and the PCB layout portion, (I use Proteus for example) you'll definitely want to duplicate it in the schematic portion first. This way it will automatically handle all of the common nets, and you can designate a value for every component on the board.

In my software, if say I want to just make to copies in the PCB part, it's POSSIBLE, but it starts getting messy. It will draw rats-nest view connections between the identical parts and pins between the two copies, and then you have to remember to not accidentally connect the same parts (unless it's power obviously). I've done simple boards this way, but it's not the cleanest. It also makes it hard to update the schematic and bring those changes back into the PCB layout side.

Also, there is some in-between ground between the high speed digital signals mentioned above, and something slow like a modulator.

If you want to do a dual VCO for example, you want to make sure you separate the two oscillators as well as possible, run their own sets of power traces from entry, that do not connect anywhere else on the board, you need plenty of bypassing and probably a bit of bulk capacitance. Dual VCO boards in this example can soft-sync to each other in unwanted ways if the layout isn't done carefully.

All this said, I've made quite a few dual boards and even full system type boards that all work quite well. You just need to take a bit of extra care is all.
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