hi!
i'm tying to figure out a way to switch 125 relais via one arduino - is that possible? i used the ShiftOut tutorial earlier - is it possible to extend it to that amount?
thank you for every idea,
emanuel
Hello Emanuel,
I think you should able to increase the number of shift registers to control that many relays. I just modified the code in the ShiftOut tutorial to support three shiftregs by adding a third array and code to read that array. I think there may be a more elegant solution but I'm just learning also. My goal is to sequence 80 lamps.
arta
In theory, I'd say yes. You would need a demultiplexor with (at least) 7 selectable inputs+f (2^7=128) so that's 8 pins, and arduino has 13, right? It would probably get complex, but it should be possible...
This is just the thing for a row of 74HC595 shift register chips. You'll get 128 outputs, each capable of driving 35mA. If that's enough to drive your relays directly, the just connect 'em up and add a back-EMF protection diode to each one. If it's not enough current, then you'll need to add a driver chip such as the ULN2803.
I think the biggest problem with this circuit will be managing the huge number of connecting wires!
You should consider doing it like people do with all those LED matrix setups.
Two 8 by 8 matrix'es = 128 outputs.
You should also think modular. Otherwise it will be a mess
hello MikMo!
thanks for your reply.
do you have alink for me regarding the LED matrix setups?
hey art, anarchocomputer,
so the schematics for 16 shiftouts would look just like the one for 2?
thanks for your help,
emanuel
yep, keep adding the 595's with the clock and latch pins going to the arduino and the pin 9 of the 595 to the data in pin of the next 595. I'm just beginning to get an understanding off how the data gets moved through the shift registers.
arta
I don't think it would be wise to use a matrix multiplexing scheme. The relays would be switching on and off all the time, at the speed of the multiplexing code. This might (maybe) work with old-fashioned coil relays, but won't work with solid-state relays. It'll most likely make the coil relays chatter, too. And remember that the average relay coil current will be reduced quite a lot. All in all, he's better off using 595 shift registers and no multiplexing.
allright, we just realized, that we will need 180 switches instead of 125. would it be possible to start a second chain of 74HC595 chips?
best,
emanuel
would it be possible to start a second chain of 74HC595 chips?
Yes but there is no point just make the shift register longer by chaining them together. As they are relays (please note how this is spelled) they are not going to be turned on and off very fast so updating them is not going to be a problem.