Controlling Relay

txaggie

Excellent! Then that is what I shall do then. I really appreciate all your help and patience.

Thanks,
Scott

PJAllen

OK, sounds like a plan.
Be well.

txaggie

PJ, I have one more question I was thinking about. The 5V regulator drops slightly with all 3 relays on and since I am trying to use a stable 5V reference voltage for my ADC, would you recommend using a separate regulator for my ADC, or is there a better way to keep that Vref stable?

Thanks,
Scott

PJAllen

I was thinking about that and mentioned it earlier on, but didn't want to feed that spectre.
There's V_cc available from the Stamp itself, via the App_Mod connector, and the ADC shouldn't demand much from it. Barring that, I'd make a separate supply for the relays; a good old 7805 with a fair heatsink.

txaggie

Thanks PJ. Unfortunately, my BOE doesn't offer thee Vcc from the actual stamp on the appmod connector, just Vdd from the 5V reg. Nothing a wire and some solder can't fix. Question: should I use the stamp's Vcc to actually power the ADC or use it just for the Vref on the ADC and power it from the external reg?

Thanks,
Scott

PJAllen

Whoops -- sorry, didn't have one in front of me; the BoE and the HWB merge in my brain sometimes.
For both, as I see it. Neither the ADC nor the reference should be current hogs.
If you can pick off the V_cc, make judicious use of it. It's the Stamp's own reg. An ADC is ideally high-impedance, when used as intended it shouldn't become a part of the circuit being monitored anymore than a good voltmeter would.
The MCP3204 spec sheet states operating current <500uA (that's < 1mA).

The V_cc is used/available on the HWB and the BS1 for just this sort of thing.

PE - You may consider a TL431 or similar for a low-current reference. V_cc isn't a reference as such, it's a power supply, but it should be pretty solid. All the better reason for keeping your base currents as low as practicable.

PJAllen

One more thing, the LT1121, the Stamp's on-board regulator and source of this "V_cc" on pin 21 is spec'd for "150mA", but just take it easy, keep things real rational all the same.

txaggie

Thanks PJ! I dug around in my electronic drawers and found a couple 7805s and LM317s, so I will probable go with what you suggested earlier. That and you have scared me away from using the stamp's Vcc. I am not very confident and don't want to blow a $75 micro-controller on account of me screwing something up. I also found a fairly small, open frame 9VAC 1.6A brick to use as my supply for when I move this project to an etched pcb and enclosure, so I will have plenty of overhead. Like you said, I could use one regulator for the relays and the other for rest of the circuitry.

Thanks for sticking with me while I sort this out!

Scott

stamptrol

Once you get your transistor successfully switching the relay on-off, you may also find that there is some coupling of the AC due to the capacitance of the experimenter boards and other conductors physically close to the AC line.

You may have to put a small filter capacitor on the Stamp's Reset pin and/or on the DC supply at the Stamp.

Cheers,

txaggie

Thanks for the suggestion Tom! I am putting a 1000uF, 10V cap on the reset pin and also on each of the two regulators, just like the BOE has. Do you suggest adding a smaller cap on those as well? What do you mean when you say "coupling of the AC"? I will be bringing AC directly to the board to both power the brick for the circuits and also for the relay that will switch the power for the charger. I am trying to keep it as far from the rest of the circuitry as possible. Is this something I need to be concerned with? I am in the process of moving the circuit from the breadboard to a prototyping solder board and will post pictures on Monday.

Thanks,
Scott