I'm trying to hang an 8-way relay-driver off a USB port, with the circuit b= eing bus-powered.=20
The relays in question need at least a 9v signal, and they can be at the en= d of a 25' wire (DB9DP9). This part is fixed because it's an off-the = shelf part.
The first attempt was to try using an ICL7660 (since I had them lying aroun= d) in voltage-doubling configuration. That worked fine until I actually wan= ted to use the relays [grin]. The 7660 could produce 9v with no load, but a= s soon as I connected just one of the relay pins, the voltage dropped to ~4= v and the relay failed to switch.
So I was wondering if the MAX232 would do any better - I know it's not what= it's supposed to be used for, but all I really want is +10v from the USB's= +5v that will drive 8 relays... I'm supposing that the RS232 drivers would= probably be specced to drive the voltage down a long serial wire anyway, s= o maybe they'll do better ?
If it comes down to it, I can have a separate power-input to the controller= (and basically make it not bus-powered) and then there's no problem, but i= f there's a good way of avoiding that I'd like to know about it :)
Thoughts, anyone ?