Call me daffy!

[gstopp at fibermux.com]

     Okay here's a quick and dirty solution to the SPST switch-to-gate 
     circuit - 
     
     Use a hex schmitt trigger (try a 74HCT14). You'll need a +5 supply for 
     this. 12 or 15 volts will cause smoke - BTDT.
     
     First inverter: 0.1uF cap to ground on input, 100K resistor to +5 on 
     input, SPST normally open switch to ground on input. Output to second 
     inverter input. Second inverter output to third inverter input. Third 
     inverter output is gate output.
     
     Second inverter output to fourth inverter input via 0.47uF cap. 100K 
     resistor to +5 to fourth inverter input. Fourth inverter output is 
     trigger output, 20 ms wide, on rising edge of gate.
     
     An R/C delay thing can be placed between the first inverter and the 
     second inverter, to delay the rising edge of the gate and the trigger 
     along with it. This goes as follows:
     
     First inverter output to diode 1 anode. Diode 1 cathode to 1M pot end. 
     1M pot wiper to second inverter input. Second inverter input to 0.47uF 
     cap to ground. First inverter output to diode 2 cathode. Diode 2 anode 
     to second inverter input. The 1M pot is the delay pot.
     
     You may recognize the delay thingey as an AR envelope generator with 
     the release resistance = zero. Two inverters are not used and can be 
     used as extra gate or trigger output buffers. If you don't use them, 
     just don't let their inputs float - tie them to ground or something.
     
     The R/C at the input of the first inverter, where the SPST switch is 
     located, can be messed with. It's there to mush out any spikes from 
     the switch bounce. If you get too liberal with the mushiness (e.g. 
     make the R/C real big) then you will start to notice a fall time 
     extension of the gate as you release the switch. Fortunately the 
     critical timing on gates and triggers is their rising edge, and not so 
     much their falling edges.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: Call me daffy!
Author:  Bob Zimmer <bzimmer at voicenet.com> at ccrelayout
Date:    11/1/96 1:06 PM
     
     What I'm hoping for is the standard +5 levels.