Quick question about R.G.'s relay circuit

[sjaltenb]

I was having clicking problems with my relays so i made up this circuit as shown:

http://www.geofex.com/article_folders/rmtswtch/rmtsw.htm 

in picture 3 (without the LED section)

I then hardwired the 9v to the relays, and passed the ground signal through the circuit design. I then have a switch that either connects the circuit to ground or does not.

However, the relay will not throw. I have an additional diode to protect against backward currrent on the relay board already, could that be the culprit? The relay circuit itself is connected to ground at all times.

so i guess my question is, the +on/-off lead should be a switch that does or does not connect to ground, which will then throw the relay, right?

[R.G.]

However, the relay will not throw. I have an additional diode to protect against backward currrent on the relay board already, could that be the culprit? The relay circuit itself is connected to ground at all times.

so i guess my question is, the +on/-off lead should be a switch that does or does not connect to ground, which will then throw the relay, right?

The +on/-off signal must be driven high to provide base current to the transistor which switches the relay. If it is simply grounded or not, the transistor, and hence the relay, will never switch. The resistors R1 and R2 have been selected for this to be the right base current for a +on/-off signal of 0V for off and +12V for on. It may work fine at 9V, but you may need to reduce the value of R1 and R2 at 9V. It depends on the gain of the transistor and how much current the relay needs.

Some relays have either an internal protection diode across the relay, or otherwise require the coil to be connected with a specific polarity. Others do not. Check the datasheet for your relay.

[sjaltenb]

Thanks R.G.

I went ahead and rebuilt the circuit a little more carefully and added the LED section. If i add voltage (9) to the circuit, the LED stays on, and the relay throws (no matter which side I connect the positive and negative leads to on the relay.

So, the circuit works, but it is staying On all the time, not matter which side the control is attached to. I am using components as listed, 1n4148 and 2n3904.

Any thoughts? Thanks!