ne555 timer circuit not working

[owen02]

Hey im making a timer using ne555 ic and when i made the circuit on bread board it worked fine and tried to transfer it to vero board and it dindnt work is there any reson why it didnt work i checked the traks for solder but there wasn't any . Attached are photos of the veroboard :

 

[betwixt]

That doesn't look right at all. A schematic diagram would help us see what you are trying to do.
You have it wired as a monostable with a capacitively coupled trigger with a pull-up resistor at the input. The output pin is connected directly to what I presume is the base of the transistor so either you could be is shorting the output through it's EB or CB junction or you can potentially damage it with your connection to the puzzle.

Brian.

 

[owen02]

this is the original drawing :

 

[betwixt]

My assumption was correct but there is no transistor on the schematic and there is one on your board. How you connect it makes the difference between the circuit working or not. Please show on the schematic how you have the transistor wired to it.

Brian.

 

[Audioguru]

Also show the part number of the transistor so we can see if its pins are EBC North American, CBE European or ECB Asian, and so we can see if it is an NPN. a PNP, a Jfet or a Mosfet.

The output current from the 555 can be as high as 200mA. If you connect it directly to the base of an NPN transistor that has its emitter at 0V then more than 200mA will flow in the base-emitter of the transistor which will probably destroy the transistor and might also destroy the 555. A current-limiting resistor must be added between the output of the 555 and the base of the transistor.

 

[owen02]

Is this Correct ???

 

[betwixt]

My guess is you are trying to make the LED flash quickly for about a second then stay off and this is triggered by closing the switch.

If I'm right, the schematic is wrong, the output of the first NE555 should go to the reset pin on the second one and it's supply should be connected all the time. However, I can't see the logic in enabling the second NE555 (wired in astable mode) with a one second pulse when it's own frequency is so slow you may only see a brief flash anyway.

Can you explain what exactly the circuit is intended to do?

Brian.

 

[owen02]

the circuit is intended to switch on the flashing led circuit for a piriod of time even when the switch is still pressed... Is there any way that there is a diagram for how the circuit will be on veroboard???

 

[Audioguru]

Your NPN transistor (that has no part number) is upside down. The collector of an NPN transistor must be positive compared to its emitter.
Your transistor should be a PNP transistor that works perfectly as a switch when its emitter is positive.
But I was correct to see that without a series current-limiting resistor between the output of the left 555 and the base of the transistor your circuit will destroy the base-emitter of the transistor and probably also destroy the 555.

Another problem with your circuit is that the transistor is trying to pull the 0V pin 1 of the right side 555 to the positive supply voltage instead of to 0V. The positive power supply pin 8 is NEVER powered.

Why do you need the transistor? The output of the left side 555 can directly drive the reset pin 4 of the right side 555.

 

[betwixt]

Do as Audioguru and myself suggested earlier - remove the transistor completely, connect the output of the first NE555 to the reset pin on the second one. Then connect the ground and supply pins of the second NE555 permanently to the supply rails.

The first circuit NE555 is a monostable and the capacitor at pin 2 ensures it only gets a brief trigger pulse at the moment the switch is closed. The time interval set by the first NE555 then enables the second one to oscillate (astable mode) which flashes the LED. With the values you show, it should flash approx 5 times a second with a 66% duty cycle and for about 7.5 seconds from when the switch is closed.

I can't help with a Veroboard layout but it should be very simple.

Brian.