relay power supply question

firealarmfreak

Hey my relays that were soldered recently broke (wires came off solder) The only other relays I have access to where i live are 12 VDC 5 amp dpdt relays in which fit on a breaboard (checked).

My only problem is I was using the 5 volt regulator on the board of education by parallax before to power them because my last ones that broke were 5VDC.

I do have a 12 volt transformer so can I still have the basic stamp pin activate a tranister and then actiavte the relay only using an external power source to energize the coils? in other words, instead of using VDD and VSS on the Board of education, just use the + and - on my 12 volt power supply.

Thanks.

Chris.

Mike Green

You do need a common ground. The (-) of your 12V power supply has to be connected to the BOE Vss. You do need to wire them (transistor and relay) like the diagram that I referred you to. If you leave out the diode, there's even more chance that the reverse EMF spike will eventually destroy your switching transistor. It can also cause the Stamp to reset.

NewAgeServer

IS there any way to prevent the Stamp from resetting itself? Me and firealarmfreak are both builsing systems that pulse fire bells and it keeps resetting like that. Is there any way we can prevent it from doing that at all?

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I'm not new at basic stamp, but i am new at the LCD AppMod

Mike Green

1) You need to have a stable power supply for the Stamp.
2) You need to have some kind of relay or switching transistor to actually turn the bell on and off
3) All relays and motors have to have a reverse connected diode across the coil or motor.
4) The Stamp and relay or Stamp and motor (if switched by a transistor) need to have a common ground,
but you have to avoid ground loops. Best is to have one common ground point, usually at the higher
current power supply with a heavy wire to the high drain device and possibly smaller wires to the Stamp and
its power supply. Sometimes a capacitor (like 0.1uF ceramic plus a 100uF to 1000uF electrolytic all with
appropriate voltage ratings) across the motor/bell will help.
The general idea is that the fire bell is a source of high electrical noise and, if this noise gets into the Stamp's
power supply, it can cause a reset by dropping the supply voltage below about 4.2V. Noise can also get directly
into the Stamp's reset circuitry and noise spikes can get into the I/O pins sometimes and this can occasionally
cause resets.
Please read the previous thread with "firealarmfreak". All of this has been discussed before.

Franklin

With all the problems you are having you might consider using these en.wikipedia.org/wiki/Opto-isolator

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- Stephen

firealarmfreak

I figured out why the stamp was resetting.

It was because I did not have a resister between the pin and the base on the transister. I am still confused on how to connect the diode and like you all said a diagarm is worth a 1000 words so could someone make me one please?

Mike Green

You have already been given a link to a complete and well done diagram in the Nuts and Volts Column. Please do not ask for something if you are unwilling to take advantage of it.

firealarmfreak

hi i wired it up as you said mike, and the relay energizes when i plug it in but it does not go on and off when i program the BOE. ???