The lowest voltage relay at Radio Shack that I could find is 5v, and I tried them out and predictably they wouldn't work. So I'm in the market for a low voltage relay.
Can anyone tell me if these will work? Or if there's another one that I should consider?
Look at the datasheet for the TC4069. Its output is limited to a few mA, depending on the voltage supply. Its highest output is listed as 12 mA (see: p.2 of datasheet). It is only 4 mA at 5V. Based on that 164988 requires too much current.
The 127790 requires 3 mA at 3V, so you are just at that limit for voltage, but OK for current. I'd give it a try.
I'm actually hoping to build two different controllers with these relays. The first carries very little DC current: there's a serial port circuit I use very often, it shorts one of the pins on the serial port to ground. So with this one I'll be using the button to control things on my computer. Here's the circuit:
The other circuit connects and external button to my digital camera. The CHDK open source firmware for Canon Powershots lets you hook up an external button to the camera's USB input. It's very clever: since the camera senses when its connected to USB power, the firmware lets you connect an external button to the camera via a hacked USB cable that carries 5v, tricking the camera into thinking its connected to a computer. So that circuit will be 5v DC across the end of the relay.
So in a nutshell, both will be switching 5v DC, low current.
Thanks for the help. I happen to have bought the relays before getting the replies, and indeed they aren't working.
I'm about to order the Opto Isolator and the transistor... A couple of questions assuming I'm not being too much of a pest:
- are these to connect to the LED circuit I mentioned the doorbell having, or to the IC output? Ideally I'd like to connect ot the IC output, since it sends out a single pulse when the button is pressed, whereas the LED circuit is active for about 5 seconds after the button is pressed.
- any tips on how to hook these up? I'm pretty clueless with this stuff so any tips would probably save me hours...