johnsmith123 said:
I'd like to try 3 AA batteries without modifying the code.(4.5V NO regulator.)
That is, keep the micro running in sleep mode, and wake it with a keypress on low level interrupt.
Just curious on how long the battery will last.
Hm. Not too sure how to do this calculation Right(TM), but using ideal numbers: you have 3 cells holding ~2500 mAh each, but they're in series so IIRC you don't get to add up the capacities (just the voltage). The circuit supposedly draws around 1uA in sleep mode (well, the AVR does and the rest of the thing shouldn't be adding too much to that), and
this fellow says he measured around 14mA when any button is pressed on a very similar circuit, which also seems to jibe with what the TLP434A data sheet says. So if the thing were to transmit full-time on fresh batteries, you might get 2500 / 14 = ~178 hours out of it (ignoring environmental and self-discharge issues, and ignoring the fact that it will probably stop working long before 178 hours have passed since the cells' voltages will likely drop too much to keep going). I'm assuming alkaline batteries here. Also, assuming that the the thing will only transmit at most once per day, on 5 days out of the week, for long enough to turn on your LED/buzzer thing--maybe a second?--that's...um...5 seconds a week at 14mA draw, and 604,795 seconds a week at ~1uA. I'm sure you can see where I'm going with this.
n.b. Somebody who sees problems with my math/assumptions please beat me (gently) with a clue stick if I really screwed that up.
I installed the transmitter approx 170' away from the receiver, and it works like a charm. I am using a 3" copper wire for an antenna for both RX and TX (the center conductor from an RG6 cable)
That's a 1/8 wavelength antenna; the original designer recommended a 1/2 wavelength; I don't know how much of a difference it would make to your application. A 1/4 wavelength antenna might be a nice compromise at 6-7".
The transmitter is outside, in my mailbox. When the mailbox is opened, it signals the receiver to turn on an led and beep a buzzer. The led stays lit until reset. We can't see the mailbox from the house, so it's nice to know whether we have mail or not.
Neat! It occurs to me that I have no idea where you are (you haven't filled in the location in your profile) but do you need any kind of license to operate on that frequency where you are? If the thing is only sending one pulse a day then it's unlikely that anyone will really notice, though.
I am also curious to know how the circuit will perform in the freezing cold winter.
Hm. The TLP434A is rated -20C to 80C, and the AVR90S2313-10 can be rated at 0C to 70C for the AVR90S2313-10PC and AVR90S2313-10SC, or -40C to 85C for the AVR90S2313-10PI (
**broken link removed**.
It also depends on the batteries; chemical reactions slow down in cold temperatures. I am not too sure what the best cells for your temp. range would be. I also can't tell you about how the crystal will respond, although I'd guess it will slow a bit. Enough to affect the circuit? I don't know.
Torben