analog switching

[egasimus]

I'm building RunOffGroove's Mr. EQ - however, I'd like to add some extra functionality, namely latching tactile switches with LED indication instead of mechanical SPSTs.

1. Switching: Since the switches are to ground, do you think it will work with garden variety BJTs? If not, I'll resort to a 4066.

2. Latching: This is quite unclear to me. It probably can't be done easily without CMOS chips? So - what's a good quad flip-flop IC, and how do I use it in this application?

[slacker]

I think BJTs would would work fine. For some examples of switching have a look here http://tech.thetonegod.com/switches/switches.html you should be able to do what you want using the flip-flop examples there. The CD4013s are dual flip flops so you'd need two, plus an inverter chip either another CD4049, CD4069 or CD40106.

[amptramp]

1. It would probably work with either type of switch.  You can expect the 4066 to have about 100 ohms of resistance switching to the negative rail, so that effect should be negligible.  BJT's could also be made to work.

2. Latching would best be done with a pair of 4013 dual flip-flops.  You have the opportunity to use a power-on initialize to ensure that all latches come up in the same state and you can drive indicator leds through a buffer.  Feed the /Q output back to the D input to make it toggle (i.e. change state every time the clock is pulsed).  Every time the clock goes up, this will toggle, so you may want to tie switches to the plus supply.  Use an RC circuit to debounce the switches.

[egasimus]

Thanks, I'm glad there's some sense in the ideas I've been considering
Do I need to bias the transistors to Vcc/2? And I was really hoping for something a bit more compact regarding the flip-flops. Is there perhaps a chip with four independently clocked flip-flops with /Q and D pins internally tied together, or is this too farfetched?

[merlinb]

namely latching tactile switches with LED indication instead of mechanical SPSTs.

If you're using latching switches then I wouldn't expect you to need flip flops as well (?). Normally you use flip flops for non-latching switches. Discrete FETs could take the place of the original switches...

[egasimus]

Well, I don't know of any tactile switches that are actually mechanically latching And I'd prefer not to use FETs - they're too hard to source for me, that's why I'm asking about BJTs.

There's so much I should know, yet I don't... Meh :/