Hi guys,
If anyone out there can help me I would definitely appreciate it. I’ve been out of electronics for about 20 years now so please bare with me if my question seems overly simple. What I’m trying to do is build a circuit that would fire 2 relays alternating within a second. I found this nice circuit on the web unfortnately your system wont let me post a link to the site of the diagram because I haven't posted 3 threads yet, it is a bi-stable Multivibrator. Please bare with me as I try to describe the circuit layout. A 9vdc power supply, from the positive post a line goes to 4 points P1 is R1 470 ohms to the cathethoide of LED 1. LED 1’s anode connects the collector of Q1 transistor 1. Q1 transistor 1’s emitter goes back to Negative of 9v. P2 is R2 a 10k ohms resistor, it connects at the base of Q1. P3 is R3 a 10K ohms resistor, it connects at base of Q2. P4 is R4 470 ohms to the cathethoide of LED 2. LED 2’s anode connects to collector of Q2. Q2‘s emitter goes back to Negative of 9v. From the collector Q1 the positive end of C1 is connected, C1 is 100u the negative end is connected to the base of Q2. From the collector Q2 the positive end of C2 is connected, C2 is 100u the negative end is connected to base of Q1. The transistors are NPN type. I apologize for my description of the circuit, I did my best. I built the circuit as shown and used a 6v dc power supply and diodes fired at an acceptable frequency. But when I connected to my 12v dc source it fired at a frequency that was too high for me to use. If I get the circuit to work I will be firing the relays from the collectors of the transistors. Can anyone give me any advice of how to adjust my resistor and capacitor values to work with a 12 v dc source and result with the same frequency? Or is there an easier way to fire the relays? Thank you so much for your advice in advance.

 

I think that you can post schematics even on your first post.

It looks like a standard multivibrator. If you increase the 10k or the 100µF capacitors the frequency will be reduced.

You may be able to connect the relays in parallel with the resistor / LED combinations, but make sure to add a freewheel diode to each relay.

Otherwise, leave the multivibrator as it is and add two more transistors to drive the relays.

 

Diver300 thank you so much for your help. I just want to get a few things clear in my mind. First the free wheel diode, there is a diode built inside of my relays that is actually parallel to the coil inside. Is this the same as the free wheel diode you referred to? Also, you advised that relay should be parallel with the LED. Are saying that the lead of the relay that triggers the internal switch should be at the point between the resistor and the LED and the ground lead of the relay should be at the collector of the transistor? (This would be true parallel with LED) Or should the triggering lead of the relay be connected between the resistor and the LED but the relay's ground lead go to the negative of power source bi-passing the transistor? Thank you so much for your advice.