Post Number: 203
|Posted on Saturday, March 25, 2006 - 7:05 pm: || |
I found this old, but still working pager by
motorola, and when i tinkered it i found this
shiny oscillator, and took it out the board.
It's a "37B09", "it's 17.900 mgh", and another
one written below is "(M)T9450". The (M) by the way
is the motorola logo. it has four pins, i dont
know what are the working pins. it is square-ish
Post Number: 18
|Posted on Sunday, March 26, 2006 - 6:36 am: || |
17.9MHz is in the 16-meter shortwave band. Your normal AM/FM radio won't pick it up.
Post Number: 213
|Posted on Wednesday, March 29, 2006 - 4:05 am: || |
It seems that i don't know it, but i do. I bought
this am radio receiver which it suggested by
simon in the computer controlled transmitter.
My only problem is i don't know what pins to use,
i know you can experiment with the pin
combinations but it might destroy the oscillator.
It merely needs 1.5 v all i need is a 1.2 v battery
to experiment with it safer. And luckily beside
the oscillator on the PCB i found this 20 mhz
receiver, which i believe is used to receive the
incoming messages from the service provider.
I can easily change the frequency (a bit) by putting
I. Dimov (Overrider)
Post Number: 42
|Posted on Monday, April 24, 2006 - 1:39 pm: || |
Instead of spending so much time on thinking of expensive/rare/hard to make substitutes, why not use 555 or 556 timers?
Simon Quellen Field (Sfield)
Post Number: 1175
|Posted on Monday, April 24, 2006 - 2:27 pm: || |
The Intersil 7555 datasheet lists 1 Mhz as the far upper bound
for the part. At that limit, I would not expect the accuracy to
be all that good, expecially since there is no crystal in the
feedback loop. It will also change frequency with temperature.
Add to that the problem that it does not produce symmetrical
square waves, and you have a poor choice for an AM transmitter.
You could configure one to run at 540 kilohertz, and just keep
adjusting the receiver as the transmitter drifts, but that is
not kind to the people who share your airwaves.
The quartz crystal oscillator is $3.00. The 7555 is $0.50, plus
the resistors and capacitors needed to make the circuit. That
just isn't much of a difference to worry about. If $2 is too much
money, you have other problems to worry about. For $5 you can have
the oscillator, the RS232 socket, and an alligator clip, making
it even cheaper to do the project.