making your own demux has got me stumped

Thread Starter

ranch vermin

Joined May 20, 2015
85
So a mux is fairly simple if its just reeling the parallel signals onto a single signal. But reverse has the problem that if you just do that you end up with pulses.

So I guess maybe you go through some kind of accumulator capacitor/voltage doubler setup - to get a bit of voltage back on the dropouts.

I guess thats what youd do. As long as it wasnt needed 100000 times maybe a few capacitors wouldnt hurt it. :)

Since im planning on switching high voltage relays with the signal, its damn important i keep those switches closed and open when i need them to.
 

crutschow

Joined Mar 14, 2008
25,132
If you want to keep the output of the mux constant when the output is not being addressed then you need a latch at that output.
An addressable latch, such as the 8-bit CD4099, which has 8 latched outputs, should work for you.
If you need more than 8 outputs you can cascade them, using the WRITE DISABLE input to disable writing to the chips not active.
Are you using a microcontroller to generate the control signal?
 
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Thread Starter

ranch vermin

Joined May 20, 2015
85
Yes, its cpu based - coming out of an ordinary usb, so i need to split it parallel out - and mux it back in the read wire.
ah addressed? do you mean using the pulses to set feedback flops - and using memory to do it. I didnt think of that.
 

crutschow

Joined Mar 14, 2008
25,132
Yes, its cpu based - coming out of an ordinary usb, so i need to split it parallel out - and mux it back in the read wire.
ah addressed? do you mean using the pulses to set feedback flops - and using memory to do it. I didnt think of that.
Not exactly.
You give a 3-bit address to the CD4099 and then a data bit to set the latch at that address output.
The latch is the memory.

You could use a USB to parallel port adapter to generate the required parallel commands for the CD4099.
 
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Thread Starter

ranch vermin

Joined May 20, 2015
85
USB to parallel port adapter? that IS a demux. :)
its a digital signal, but it closes an analogue voltage relay, given the right temporal pattern.
 

crutschow

Joined Mar 14, 2008
25,132
USB to parallel port adapter? that IS a demux. :)
its a digital signal, but it closes an analogue voltage relay, given the right temporal pattern.
Depending upon the number of relays you want to control, that may be all you need. :D
But you will need a program to generate the parallel port protocol and get the desired output signals.
 
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