hi, i am new here.
i built a project for my graded unit in college, i have assembled it correctly and it was working then all of a sudden it just stopped, i traced the problem and think it might be my transistor, i am using a hex inverter with two ne555 timers to operate the switching signal within the transistor, the transistor is a 2N2905a, the power into my circuit is a 9v 600mah rechargeable battery. there is a voltage running from the pin one on the relay down to ground but the relay isn't switching. i have tried for hours to solve this myself with no good results.
any help would be really appreciated
Relayu not operating
Re: Relayu not operating
Can you post up a schematic diagram?
Does the relay work if you the coil across a suitable supply?
Is there a signal 0v to the base via a resistor? As it appears to be NPN switching the collector connects to the +ve rail, the emitter to one side of the relay coil, the other side of the relay coil to 0v.
Do you have a reverse biased diode across the coil such as a 1n4001 diode?
Does the relay work if you the coil across a suitable supply?
Is there a signal 0v to the base via a resistor? As it appears to be NPN switching the collector connects to the +ve rail, the emitter to one side of the relay coil, the other side of the relay coil to 0v.
Do you have a reverse biased diode across the coil such as a 1n4001 diode?
Re: Relayu not operating
Hi Paul thanks for the reply i will upload schematic and my version I have put on solder board I am out at the moment but have the schematic on my mobile! Be home in around 20 mins
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Re: Relayu not operating
And yes Paul the relay operates if I apply power across it.
Re: Relayu not operating
I have added two photos the emitted is into pin 2 of the relay the transistor is a pnp tran
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Re: Relayu not operating
I think you need a NPN transistor and a resistor, something like a BFY51 and a 1K resistor (between pin 3 and the base) will probably do.
Your relay coil voltage also needs to be the same as the supply voltage.
Pin 1 on a 555 timer goes to the 0v rail which isn't shown on your schematic
What does it do? It looks like a pair of monostable 555s with some sort of op amp upfront, a hex inverter just 6 not gates in a chip which is different to your schematic.
Your relay coil voltage also needs to be the same as the supply voltage.
Pin 1 on a 555 timer goes to the 0v rail which isn't shown on your schematic
What does it do? It looks like a pair of monostable 555s with some sort of op amp upfront, a hex inverter just 6 not gates in a chip which is different to your schematic.
Re: Relayu not operating
Hi,
I see you got your drawing from here: http://www.electronicshub.org/automatic ... on-system/
The schematic is wrong on a couple of points, the thing on the left looks made up and definitely isn't a hex inverter.
Pin 1 on a NE555 is ground hence if you don't connect it the chip wont power up properly.
I think when an astable is not enabled (something you can check with a meter) the output is low hence if you want your relay off and only come on momentarily a I think a NPN transistor will be more suited. Of course if the output is high then a PNP will work better.
As an aside, to measure conductivity in a liquid we don't tend to use DC as it causes electrolysis on the probes, AC doesn't but I don't know what level of electronics you are doing at college.
I see you got your drawing from here: http://www.electronicshub.org/automatic ... on-system/
The schematic is wrong on a couple of points, the thing on the left looks made up and definitely isn't a hex inverter.
Pin 1 on a NE555 is ground hence if you don't connect it the chip wont power up properly.
I think when an astable is not enabled (something you can check with a meter) the output is low hence if you want your relay off and only come on momentarily a I think a NPN transistor will be more suited. Of course if the output is high then a PNP will work better.
As an aside, to measure conductivity in a liquid we don't tend to use DC as it causes electrolysis on the probes, AC doesn't but I don't know what level of electronics you are doing at college.