View Full Version : controlling relay w/a stamp?

04-08-2007, 05:13 AM
i'm trying to make a project where different sound sources are inputted and either one source or the other will be outputted. i'm trying to do this with a bs2 & a relay and am having a lot of trouble because the lowest voltage relay i could find was a 5V, however, even with a transistor to ramp up the voltage coming from the stamp and into the relay, the best I can get it up to is 4.5 V, therefore the relay won't work because it's not getting enough power. Any suggestions?? I was trying to do this previously with a digital potentiometer instead of a relay but had even more problems with getting that one to work..
thank you,

Robert Kubichek
04-08-2007, 05:28 AM
Why don't you go fully digital with digital controlled analog muxes...
Here is a link to one that has 16 analog inputs independently controlled/isolated from the other;

focus.ti.com/lit/ds/symlink/mpc506.pdf (http://focus.ti.com/lit/ds/symlink/mpc506.pdf )


T Chap
04-08-2007, 05:31 AM
Can you post your schematic? Most relays that are rated at a voltage, will actually turn on at a lower voltage.

There are other options to switching audio like Jfet transistors and audio switching IC's. For simplicity, you should be driving an NPN transistor by the Stamp, the relay has as fixed positive voltage on one pin, the other pin gets sent to GND by the NPN transistor which is driven by the Stamp pin. Google NPN relay driver, there will be tons of stuff to look at.

Post Edited (TChapman) : 4/7/2007 10:35:38 PM GMT

04-08-2007, 07:30 PM
I have built my own SSR's before to control X-mas lights, the nice thing about them is they can switch using about 3V since there switched by an OPTO isolator with Triac output. like this

·http://rds.yahoo.com/_ylt=A9gnMiRI3xhGFGAAfSujzbkF;_ylu=X3oDMTA4NDgyNWN 0BHNlYwNwcm9m/SIG=12ug443kr/EXP=1176121544/**http%3A//instruct1.cit.cornell.edu/courses/ee476/labs/s2006/optoisolator.pngThen you will just add another transistor to this out put if your going to switch higher voltiges, also you would need to add a few resistors. I realy don't get what your trying to do so i hope this might help or somthing.

There are no Undo buttons in life.

04-08-2007, 09:25 PM
Have a look at this thread...

'Necessity is the mother of invention'

04-20-2007, 09:51 PM
You might want to look at these relay boards they sound like they are exactly what you are looking for at a good price

04-22-2007, 04:48 AM
The simplest solution is to use an FET, like a 2n7000, with the source tied to ground, the gate to your stamp pin, and the drain to the relay coil. Hook up the other side of the coil to +V. and don't forget the snubber diode across the coil.
But, I am a little confused since I have switched relays directly from a HIGH on a BS2. coto makes 5V coil relays with built in diodes....

Mike Green
04-22-2007, 05:23 AM
I believe the 2N7000 has a relatively high gate threshold. It begins to switch on at about 2.1V, but won't carry any significant current until the gate voltage gets to 4-5V. Use a logic level threshold MOSFET which switches at a lower threshold.