Hi, I'll try to explain this the best I can. I'm a newbie, so bear with me.
Scenario: I have a Force Sensitive Resitor that will run through a LM358 that will trigger a pn2222a NPN transistor, which will activate a relay.
I have laid out the circuit according to this data sheet on page 22, http://resenv.media.mit.edu/classes/MAS836/Readings/fsrguide.pdf
Goal: When I press on the pressure sensitive strip, I want it to activate a relay based on the set threshold.
Problem: Right now, for some reason the transistor is being kicked on by the op amp without pressing the strip, But when I press the strip, it turns off the transistor. I'm using the inverted input as a comparator to set the trigger point.
Setup: Operating Voltage is 24v.
I'm running a voltage divider to feed 5v into the strip which goes the non inverted input. Someone said they burned a strip from running 24v into it. That's the reason i'm running a voltage divider for it.
I have a 10k pot that gets 5v from the voltage divider that goes into the inverted input. This is used to adjust the threshold. I will be replacing this with a fixed voltage divider once I figure out the threshold value.
I'm feeding 24v into the LM358, the output goes to a pn222a transistor, which triggers a 24v relay. I can trigger the transistor manually by feeding power into the base.
Following the circuit above this is the values I'm using for the components.
RM: 10k
R1: 10k Pot
R2: 10+20k
R3: I had a 4.7k, but had to remove this, as it wouldn't trigger the transistor for some reason.
q1: pn2222a running 24v
Relay 24v NC
D1: I don't have this in place.
This seems like a fairly simple circuit, but i'm not sure what i'm doing wrong here. Maybe the resistor values are off because of the 24v.
Any help or comments is highly appreciated. Please let me know if I can clarify anything.
Thanks
Scenario: I have a Force Sensitive Resitor that will run through a LM358 that will trigger a pn2222a NPN transistor, which will activate a relay.
I have laid out the circuit according to this data sheet on page 22, http://resenv.media.mit.edu/classes/MAS836/Readings/fsrguide.pdf
Goal: When I press on the pressure sensitive strip, I want it to activate a relay based on the set threshold.
Problem: Right now, for some reason the transistor is being kicked on by the op amp without pressing the strip, But when I press the strip, it turns off the transistor. I'm using the inverted input as a comparator to set the trigger point.
Setup: Operating Voltage is 24v.
I'm running a voltage divider to feed 5v into the strip which goes the non inverted input. Someone said they burned a strip from running 24v into it. That's the reason i'm running a voltage divider for it.
I have a 10k pot that gets 5v from the voltage divider that goes into the inverted input. This is used to adjust the threshold. I will be replacing this with a fixed voltage divider once I figure out the threshold value.
I'm feeding 24v into the LM358, the output goes to a pn222a transistor, which triggers a 24v relay. I can trigger the transistor manually by feeding power into the base.
Following the circuit above this is the values I'm using for the components.
RM: 10k
R1: 10k Pot
R2: 10+20k
R3: I had a 4.7k, but had to remove this, as it wouldn't trigger the transistor for some reason.
q1: pn2222a running 24v
Relay 24v NC
D1: I don't have this in place.
This seems like a fairly simple circuit, but i'm not sure what i'm doing wrong here. Maybe the resistor values are off because of the 24v.
Any help or comments is highly appreciated. Please let me know if I can clarify anything.
Thanks