Hey all, i have been up and down trying to figure out why this is happening to me! This is the stats:
- Small Signal Transistors NPN 30V 100mA HFE/8
- 1k resistor
- 10k resistor
- 12v SPDT relay
- 1N4004 400v 1a standard rectifier
I am modeling it after this schema: **broken link removed**
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Here is the picture of my board... **broken link removed** **broken link removed**
I supply the 12v to it & the 5v. I get the these values:
Emitter: 0v
Base: 0.75v
Collector: 1.39v
I'm using this transistor (Small Signal Transistors NPN 30V 100mA HFE/8): SS8050CTA
What its doing is when I supply the 12v to one side of the relay it opens it up. I want it to open up once i add the 5v to the other side. I'm using an ATMEGA168 chip with the digital pin out for the 5v (but right now I'm just hooking it straight up to 5v). But for some reason its just opening without even the 5v being applied. And I'm getting those low volts from the base and collector and i have no idea why..
Actually, that's a HIGH voltage on the base if you want it to be "off". It should be near 0V for what you are describing. Find out where that base voltage is coming from.
You seem to have it hooked up correctly. Another possibility is a bad transistor.
But i want it to come ON once i supply the 5v. But nothing happens when i do that. Right now i corrected the problem with the 12v triggering it open. But still can not open it with the 5v.
I tested the relay to make sure it was working and it does. I put 12v on one side and 5v on the other and it opened. Took the 5v away and it closed.
But with the resistors/transistor, i cant do the same thing for some reason??
Yes, that's fine. It isn't really necessary with a port pin drive... but it's helpfull for this debugging stage since it will make sure the transistor is "off" when you don't apply power to the base.