1 on/off switch, 2 independent functions ?

[Slider2732]

555 on off switch

Hi there, first post here

I've hit a problem that would seem rudimentary and easily solved :|

I'm changing the circuit of an eprom based sound samples player, so that a small 1 octave keyboard can be used.
Design is similar to: **broken link removed** in the 'Hardware' section.

Each key must start the 555 oscillator and also, when pressed, enable a connected resistor to change the oscillation rate of the 555...forming a rudimentary keyboard, with different value resistors (a resistor ladder could also be used).

My main problem is that of using a switch (keyboard key) to both switch on the sample playback and also set the rate. For some reason, the 555 stops or doesn't trigger.
As things currently sit, I can press the original on/off switch, which is the Pin 3 output connection between the 555 and the 4040's and then change the pitch using a resistor arrangement. The resistors all have a common tie to each other at one end and each switch is connected to the other end. This gives the rate changing desired. But, the original on/off switch has to be held down and thus playing the sample anyway, for the rate to change on pressing one of the rate change switches.
No amount of diode useage, or even an opto-isolator has solved things, so that a switch will both start the sample playback and change the rate at which it does so.

....so I thought i'd ask here

 

[onion456]

switch on/off 555

could you not use each switch to bias two transistors?

are you able to do one or the other (enable the 555, or enable the resistors) but not both?

 

[Slider2732]

on off switch using 555

The transistors solution, I thought, might carry the interaction problem along with it, because the seperation of signals still has to happen?
Can admit I have an irrational dislike of transistors themselves, noisy and flaky things and prefer chips (with similar transistors on!)..but it could be the solution.

One function is a mere complete of a signal path, as a switch would do. The other is to control the resistor value of the 555 oscillator for the pitch.

I'm able to press the original on/off switch, that used to just play the sample at the rate I would set on a VR, then if I press one of the switches (keyboard keys) it will change the pitch. Each key works, but only if the unaltered original on/off switch is pressed along with it. Taking the on/off switch out of the circuit and replacing with firing from the keyboard switches is the aim.
Changing things around, by swapping the connections to the resistors, resulted in the 555 grinding to a halt when a switch was pressed. Hence, it all needed redoing.

One area i'm looking at too was that I used a 4N35 for the optical seperation trials, whereas i'm now thinking a Sharp PC817 type would actually work. Enabling a flow/complete of the wire that gets the 555 triggered is all it does, so the output needs to carry no line voltage. On contact of the switch to fire the 555, the resistor line would come between the PC817 and the switch, so no interaction of the two would occur. Adding a diode from each resistor would isolate each one.


Perhaps it all would be easier if I post a picture of the thing lol
(Only 3 resistors are shown, but there's 5 for the top line of switches and 8 for the bottom. Also a 7404 Hex Inverter at the bottom right, another idea for swapping on to off that wasn't likely to work, but was tried).

 

[onion456]

pc817 on-off

i guess if i could be of any further help, i'd need to know how you are 'enabling' the resistors, and how you are enabling the 555 as well- it doesnt seem at all apparent how you could get away with blending the two signals. it does seem 'rudimentary' to me to just add some transistors or relays or whatever so you can isolate the two circuits, and just control the two with one switch- easy as pie. youve already proven you can do both, as long as they are not blended. unless you know something i dont... like i dont know what kind of signals are on each line. communication across the internet is always fun, you never know the whole story, ya know =D. want to post a schematic showing how you intend this to work?

 

[Slider2732]

555 as on & off switch

Thanks onion
Oh, all and any help is appreciated.

Enabling the 555 is by connecting the output Pin 3. It may well be a route to deny the chip its +5V or deny Ground or some other method ?

Enabling the resistors has been to connect all at one end, and then, with each different key to a particular resistor, the sample changes pitch. I realise that's probably not the best method, but it seemed to work as a route for pitch changing.
I'd like to know of other methods, where an on/off switch and further processing of a voltage are implemented. 1V per Octave would be the best, similar to most analog synths, but I figured the design needn't be too difficult for simple resistor changing.

Signals per line are: One completes a wire to wire connection, the connection being from Pin 3 to the 4040's. The other affects the VR which controls the pitch of the sample, this is where each resistor is to run to.
Progress today has been to find a PC817 opto isolator and solder it up. The PC817 is connected to +5V (through 1.5k resistor) and the other leg goes to a common Ground rail that runs along all the switches and works when the switch is pressed. Now all the keys trigger the sample. It's a butt head method though, because now I have a Ground rail !

hmm, maybe the Ground rail connection can start the 555 ?


I'm open to any and all ideas..finding proven methods online might give a diagram too to work with

 

[Slider2732]

schematic 555 on/off switch

Got it..and it wasn't as difficult, as expected.
Simply deny the 555 from starting to oscillate, by denying a resistor connection!
The VR that controls speed was disabled in this way...meaning that another resistance added to the line would affect the original tuning too. Pressing a key now makes both the circuit connect up and introduces the change in pitch.
A 'cant see the wood for the trees' classic huh.

Building up the circuit now. 13 small VR's are being used as tuners of the notes.