[sdiy] Buchla Easel sequencer & CMOS output short circuit protection

[harrybissell at wowway.com]

I would always include a series resistor on a CMOS output. Probably
100 ohms would be the minimum (it would not usually be shorted often).
1K is better.

H^) harry


On Mon, 29 Dec 2008 03:22:36 -0500, Aaron Lanterman wrote
> I need to go into Buchla PCB layout rehab. The first step is 
> admitting  you have a problem.
> 
> Anyway, having finished laying out a board for the Easel's Pulser,  
> I've moved on and have the schematic for the 5-Stage Sequencer in  
> Eagle. I've included the sequencer output summing circuitry, which 
> is  on a different board in the Easel, on this board.
> 
> The schematic is at
> 
> http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2080_1_200.jpg
> 
> Two questions:
> 
> 1) There's a +15 V and +5 V brought to this board, along with a note 
>  about "eliminating the +5 V" supply by changing some things and 
> using  a +12V supply for the LEDs.
> 
> Anyone know what the chips are actually powered off of? It's a bit  
> ambiguous. If the +5 V volt supply was really _just_ used for the  
> LEDs, I wouldn't see any reason to change R9 and R19... which makes 
> me  suspect that the rest of the circuit is powered off the +5 V (or 
> +12  V)... but I really don't know.
> 
> 2) In the easel, the various NOR gate outputs at the top of the  
> schematic all go to other parts of the Easel. Here, I want it to be  
> able to operate as a stand alone module, so I'm bringing all those  
> outputs to outside jacks (if the user wants them).
> 
> Anyway, is it safe for me to do that, or should I put some sort of  
> short-circuit protection resistor at the output?
> 
> - Aaron
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Harry Bissell & Nora Abdullah 4eva