[SOLVED] Problem with relay connection

[Mrunal Ahirrao]

hi all,
Actually I am making a DTMF based appliance controller. But I am having a problem in Relay. I have used Electromechanical relay. problem is when 8870 gives output to relay it doesn't switched on! So I thought might be current is less provided by 8870. So iadded transistor between relay and IC. but then also its not. When I measured voltage across relay its 1.94V. and when i remove the IC's output to relay and measured on transistor then its 5V and again if I attach relay to transistor then again voltage drops from 5V to 1.94 V! How this is happening? please help.

 

[sequel]

what is the voltage rating of the relay...i mean the dc rating of the coil. and at what voltage is it being run from.
once the voltage is lower than the relays' rated voltage it will not be sufficient to energize the coil hence your circuit will fail.

you should also have it in mind that 8870's current output is so small...

post your circuit for further trouble shooting.....regards
sequel.

 

[chuckey]

Have you got the anti back EMF diode across the relay coil? It is required! Else the driving transistor/chip suffers from over voltage spikes ans burn out.
Frank