Trouble with 5 voltdc to 110ac relay on a homeworkboard

snap

Hi,· I am a newbe to the stamp world but would like to controll a 110 ac light with the bs2. I have a homework board and have done most of the projects but would like to make the leap to controlling a 110 load. I bought a 5v dc to 120 mechanical relay and can get the coil to set using a 4.5 volt dc external supply but can not get it to set using the high pin of the stamp. I have tried using the npn transistor that came with the stamp but don't understand why I am getting 3.8 volts when the base is LOW and less when the base is high ( although the led lights up). I then tried to use the Vin to Vss connection, this worked and would set the coil but all the time, I could not release it, the voltage never dropped below 8 volts (even with the pin set to low). I would very much apreciate it if somebody could help me on this one. If there is a recomended brand name or modle or If I should go with solid state please let me know. I know a bit about electronics so don't worry about tech talk.

Eric R

Could you·post a schematic?



I use the Crydom SDV2415 for a lot of my applications depending on the load.

I am sure someone else will chime in but as I recall, the homework board is somewhat limited due to battery power only.


Post Edited (Eric R) : 9/24/2006 3:27:52 AM GMT

snap

The load is only about 2 amps, I just want to hear the freekin click, Thank you for a quick responce, I am a water quality person and can help with aquarium or drinking water problems I am a class 2 water quality expert but can not spell.

TechnoRobbo

Ok it doesnt have to be a schematic - how about a block diagram with labels on it- Powerpoint it. Sounds like your getting a 1.2V drop across the relay. Are you using a diode across the relay and could it be backwards?

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Have Fun


TR

Post Edited (TechnoRobbo) : 9/24/2006 3:27:02 PM GMT

snap

I will work on it and attach it thanks

snap

Here is the schematic. ·The led works but it can't lock the relay coil. I hooked it up to the 9 volt out put in the bs2 and it worked but the relay would not close because even when the transister was getting the negative pulse it stayed on.
Thanks

Eric R

Ditch the LED and install the relay. Don't forget to install a diode. Looks like this was from WAM page 267. Note the LED was your load in that example but now your relay coil·will take its place.

Search Parallax for item: 27945 and use the mating G4 board as this would be a safer·way of doing this. After all, the work is done for you. Just hook up the wires.

TechnoRobbo

Wire it like this and use a rectifier diode not an LED. I'd wouldn't loose a diode altoghether because of the flyback voltage. Radio shack has 2N3904 transistors that I use with a 330ohm resistor on the base pin. That saturates it enough to switch a 5 volt relay. next thing I would suggest is to provide a seperate voltage source for the relay.·4 AA (6 volts) batterries works good.

·



If you relay want to protect your Stamp try this circuit. It completely isolates the stamp from the relay voltage. 4N35 optocouplers go for about 30 cents each.





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Have Fun


TR

Post Edited (TechnoRobbo) : 9/24/2006 10:06:34 PM GMT

snap

Thank you everyone for your help. This is my first time using any kind of forum and I can't believe how fast the answers came in. I Finally got it to work. I found out the transister that came with the stamp board was not right (I don't know if it was broken or what, although it worked with the led). I used a transister from an old radio shack 130 exper kit and it worked lik a charm.
I will rebuild it with the opticoupler to isolate it and start my projects. Thanks again to Tr and Eric.

snap

Thanks Tr, I was wondering about what you said concerning a separate power source. Do you mean on the switch side of the transister? If so I tried it and could not get the transister to work (It would not switch). If it does work does that mean that the positive feed from the BS2 pin mixes with the separate power source? (Voltage in = voltage out). Also does this mean that I could hook up say 24 volts dc to the relay and use a 24 dc coil to 110 ac.
Thanks

Eric R

To me it sounds like you do not have the grounds (- negative)·tied together from both power sources.

TechnoRobbo

I second that - the Stamps negative (Vss) should be connected with the 6vdc negative for the transistor to work

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Have Fun


TR

Post Edited (TechnoRobbo) : 9/26/2006 11:28:54 PM GMT

snap

Once again you both have have come through with quick and correct answer. I am going to start to work programming Visual Basic to make make the whole thing work from an exe program. Thanks again.
Snap

snap

For every one following this post I would like to make clear, I drew the contacts of the relay·wrong on my first schematic attempt ..Don't follow it
Thanks to the blokes who helped me tie the ground togeather.