Hey everyone,
I'm working on a circuit that will open a relay once an input signal rises above 3 volts (it will be between 0-10VDC). My plan so far has been to use an op amp to compare the input to around 3 volts (made using a voltage divider from another voltage source of 24 V). I'm having two problems however: the appears to be a constant voltage in the op amp input pins even when there is nothing is attached and even with the output being around 24VDC, the relay does not turn on (instead, it hums - i think it is rapidly turning on and off?) as there might not be enough current going through? I'm curious if anyone knows why this might be the case and how I might go about getting around it. Also, if anyone has any suggestions on how to design this circuit differently to achieve the same function (maybe using transistors?), I'm all ears. I'm working with I have around me, so I expect there might be an easier approach if I purchase more suitable components. I'm completely new to circuits so any push in the right direction will be greatly appreciated.
I was also considering buying a relay similar to this to try to 'skip' the need for an op amp: http://www.jameco.com/1/1/730-kf0604d-dc-dc-solid-state-relay-control-voltage-3-32vdc.html
Can I expect the relay to fully open once the signal goes above 3V?
Op amp: 2904N
datasheet: https://www.fairchildsemi.com/datasheets/LM/LM358.pdf
Relay: 1EHC6 12VDC
product page: http://www.grainger.com/product/DAYTON-Relay-1EHC6
I'm working on a circuit that will open a relay once an input signal rises above 3 volts (it will be between 0-10VDC). My plan so far has been to use an op amp to compare the input to around 3 volts (made using a voltage divider from another voltage source of 24 V). I'm having two problems however: the appears to be a constant voltage in the op amp input pins even when there is nothing is attached and even with the output being around 24VDC, the relay does not turn on (instead, it hums - i think it is rapidly turning on and off?) as there might not be enough current going through? I'm curious if anyone knows why this might be the case and how I might go about getting around it. Also, if anyone has any suggestions on how to design this circuit differently to achieve the same function (maybe using transistors?), I'm all ears. I'm working with I have around me, so I expect there might be an easier approach if I purchase more suitable components. I'm completely new to circuits so any push in the right direction will be greatly appreciated.
I was also considering buying a relay similar to this to try to 'skip' the need for an op amp: http://www.jameco.com/1/1/730-kf0604d-dc-dc-solid-state-relay-control-voltage-3-32vdc.html
Can I expect the relay to fully open once the signal goes above 3V?
Op amp: 2904N
datasheet: https://www.fairchildsemi.com/datasheets/LM/LM358.pdf
Relay: 1EHC6 12VDC
product page: http://www.grainger.com/product/DAYTON-Relay-1EHC6