BS2 and GSM modem (fona)

Hello all,
I just started messing around with STAMP's and am working on a car alarm project. My goal is to be able to have my Stamp Alarm system text me when it goes off and to be able respond to commands via sms. I also would like to have it text me it's GPS lat/lon when I ask it via SMS.

I have gotten my stamp to SEND me text messages ok. I got it to parse the lat/lon from GPS and send it via SMS.

The adafruit FONA has a ring indicator pin (RI) that is normally HIGH but pulses LOW for just 100ms then goes back to HIGH when it gets a SMS. Since the stamp has no interrupt I need to come up with a fun way to tell it there is a message waiting. I think the "right" way to do it would be a 4011 quad nand gate wired up to latch but I dont have any. I came up with an wacky way using a capacitor, some resistors and a diode. The cap charges through a resistor and is hooked to the RI pin of the fona via a diode. When the RI pin goes low it zero's the cap that is connected to a PIN on the Stamp. Hopefully my loop gets around to checking the pin in time before the cap recharges past 1.4volts. Any one have a suggestion on a more foolproof way or is getting a 4011 the best way? I have just basic transistors, caps, and resistors on hand.

Also has anyone else played around with a GSM modem interfaced to a Stamp? I am trying to think of how to have it handle incoming SMS's. I think its going to get messy with lots of SERIN WAIT and SKIP n. Hopefully a spam text message doesn't lock my stamp up :-o



  • A 555 timer is an excellent choice for latching or stretching a short pulse.
  • kwinn wrote: »
    A 555 timer is an excellent choice for latching or stretching a short pulse.

    Thanks for the tip! I actually have a few 555s.
    I found a good design for a "Bi-stable or "Latch" or "2-state" 555"

    I can have the fona set the latch then have the stamp reset it when ever it gets around to checking it.

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