Just another monostable 555 timer question

  • #26
vk6kro
Science Advisor
4,081
40


The transistor?
Not really.

One possibility is that the motor you are using might use less current than the relay.
If so, I guess you could switch it directly from the 555.

If you live in the US, Radio Shack have TIP31's at $1.69 and Darlington transistors TIP120's at the same price.
 
  • #27


No i live in the UK
But thanks for your help :)
I might change the 555 circuit to a latching circuit, it should work with what im making
 
  • #28
510
1


Just measure resistance of the relay coil and divide 6 volts by it to get current.
I'd just use a transistor if i were you... connect it's base to 555's output through resistor. Also I always just use opamp based oscillator or timer instead of 555, 'cause opamp is more universal and it's cheaper to just buy 10x lm324 once and use them for this sort of stuff.

Ahh and also. Relay may have damaged your 555 's output stage already. When you disconnect a relay you can get high voltage spike; you need a protective diode connected in parallel with coil so that it does not normally conduct (when you are powering the coil).

You need a 1amp or greater power rectifier diode, an LED might blow out on the first kickback. It is a refinement to the circuit so you might get away without using it.
The kickback current is equal to relay coil current...
 
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  • #29
vk6kro
Science Advisor
4,081
40


If you REALLY can't get a power transistor, you could try this:
[PLAIN]http://dl.dropbox.com/u/4222062/555%20driving%20relay.PNG [Broken]

It just uses a resistor to reduce the current to the relay coil to a safe level for the 555.
Note that the resistor has to be 1 watt as it will get warm.

A diode is still required across the relay coil.
 
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  • #30
1
0


visit

http://www.circuitshelp.com/2012/07/555-monostable-vibrator.html [Broken]

this might help you...!!
 
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