EHX Freeze Mod

[dune2k]

Hi,
I have a EHX Freeze, which I really like. One thing bugs me though, I have to tap the Bypass/...-switch twice to go from latched mode into bypass while clearing the cache (or whatever it uses ).
The general switching is quite simple, it only connects one pin to ground.

Now I need some help:
I want to add a second switch (maybe external, but that's not a big thing to realize ), that if hit automatically goes into bypass. I can't use a 3PDT switch or any other (true) bypass since that would keep the note stored, playing it again after reengaging it. So I need a simple circuit, preferably w/o a micro controller that when triggerd connects point A with point B twice for a pretty short period of time. Since I don't know the exact time frame the Freeze detects it would be awesome to be able to set that time somehow.

Thanks in advance
dune2k

[g_u_e_s_t]

you could use a dual 555 timer (556) or 74hc221.  one of the timers is set to one-shot mode, and makes a long pulse, and the other to oscillating mode at a higher frequency.  you then send the 2 outputs to an AND gate, so the fast pulse comes out twice for the duration of the longer one-shot pulse.  not the greatest solution, but should work, especially if you sync (strobe) the oscillator to the input trigger.  you could make similar things out of 74hc14's or opamp comparators and diodes.  charge up a cap when the button is pressed, and then have it take a while to discharge.

[ElectricDruid]

+1 what guest said. You need a circuit that produces a couple of pulses. You can then use a transistor across the switch you want to "press". When you feed the pulses tot he base of the transistor, it'll switch on and the rest of the circuit will think the switch was pressed.

Years ago, I learned a load of 555 timer and CMOS logic stuff like this from "Adventures with Microelectronics" by Tom Duncan. Long out of print, but now available used on Amazon for next to nothing. Buy one and have a look - there's stuff in there that will solve your problem.

HTH,
Tom

[dune2k]

Thanks for the tips, ordered the book already.
Going to start drawing a schematic some time soon.

[dune2k]

not the greatest solution, but should work, especially if you sync (strobe) the oscillator to the input trigger.

The book mentioned by ElectricDruid was really usefull, basically has the whole circuit in it. Only need to try out the proper values (waiting for them parts atm).
Now regarding g_u_e_s_ts post: How do you sync the two oscillators?

[ElectricDruid]

not the greatest solution, but should work, especially if you sync (strobe) the oscillator to the input trigger.

The book mentioned by ElectricDruid was really usefull, basically has the whole circuit in it. Only need to try out the proper values (waiting for them parts atm).

Ah, glad you managed to get it and thought it was good. I loved it, but that's no guarantee that anyone else will!

Now regarding g_u_e_s_ts post: How do you sync the two oscillators?

Been a while since I played with a 555, but don't you hold both RESET lines low until you need them? That disables the oscillators. When you let the RESETs go high, they'll both start at the same time.

HTH,
Tom

[dune2k]

Now regarding g_u_e_s_ts post: How do you sync the two oscillators?

Been a while since I played with a 555, but don't you hold both RESET lines low until you need them? That disables the oscillators. When you let the RESETs go high, they'll both start at the same time.

HTH,
Tom

Hm, I don't think that this will work. The idea behind the circuit is that you trigger one osc. once, which then lets through the pulses of the other (astable) one via the AND gate. Since I use a DPDT non-latching switch anyway I'll try to have the second (astable) osc. connected to the switch as well. When engaged it will break the connection of pin 2 and 6 which lets that half of the 555 oscillate thereby resetting it. Will let you know if that works.