Simple Light Break Detection

Status
Not open for further replies.

Thread Starter

spike1947

Joined Feb 4, 2016
293
Hi
I am going to build a light break detection sensor, as per attached schematic.

Question: I can't find a 5v relay with a coil resistance of 125 Ohms, I have some 5v relays at 70 Ohms would they work ?, also the diode 1n4004 , I have some 1N5397 would they do in place of the 4004 ? .

cheers
Spike
 

Attachments

Thread Starter

spike1947

Joined Feb 4, 2016
293
The diode will do the job OK.
What type is the transistor?
I don't think this circuit will work with a standard transistor.
Hi
Thanks for your reply, sorry left that out, it is a "N2222A NPN Transistor.
Notes on it :
The 2N2222A transistor is very much similar to the commonly used NPN transistor BC547. But there are two important features that distinguish both. 2N2222A can allow collector current upto 800mA and also has power dissipation of 652mW which can be used to drive larger loads than compared with BC547.
 

AlbertHall

Joined Jun 4, 2014
11,302
The base current for the transistor will be about 0.5mA (5V / 11k). To ensure the transistor is fully saturated the base current should be about 1/10 of the expected collector current. Even with the 125Ω relay the collector current would be 40mA. You could reduce the value of the 10k but I don't know whether the photocell would be happy with that.
Better might be to add another transistor and make a darlington pair with the 2N2222.
 
Status
Not open for further replies.
Top