Question about low voltage relays

[wrybread]

I'm trying to hack an RF doorbell to control another device. The model I'm using (made by Baoji) has a couple of LEDs that receive 3v when the button is pressed, and an IC (https://pdf1.alldatasheet.co.kr/datasheet-pdf/view/31642/TOSHIBA/TC4069UBP.html) that has a few pins that get 3v when the button is pressed.

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?

https://www.jameco.com/webapp/wcs/s...-1&catalogId=10001&pa=164988&productId=164988

https://www.jameco.com/webapp/wcs/s...-1&catalogId=10001&pa=127790&productId=127790

Thanks for any help.

 

[jpanhalt]

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.

Remember, the controlled current must be AC.

John

 

[KMoffett]

What are you trying to switch on the output side of the relay? This makes a big difference in what you need.

Ken

 

[wrybread]

Thanks for the help.

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:

https://www.danielandrade.net/2005/11/17/howto-external-winamp-control/

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.

 

[mneary]

Those Jameco parts are solid state relays. As John mentioned, they only work on AC, and they do not work on low voltage (typ. <24V) loads

Have you considered a simple opto isolator such as 4N25/6/7/8? Or, pick an optical isolator from the surplus catalogs and look up its specs.

 

[RODALCO]

Opto isolator as mneary suggest with a small driver stage via a BC 547 or 2 N2222 to drive a 5 or 12 volt relay from an external supply.

 

[wrybread]

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...