Need a 38khz pulse, is there anything better than using a 555?

[Bob Business]

Hello,
I am working on a project that sends signals via 38khz modulated IR
remote. I see some circuits that use a 555, but it seems very error
prone due to tolerances, and I don't have anything to test for
frequency. I found this chip
http://www.rentron.com/remote_control/TX-IR.htm which is a programmed
PIC that does exactly what I want for $6.00 plus $1.50 for resonator.
Are there any other options, or should I not worry and use a 555,
possible with a trimmer.
Thanks
BB

 

[CFoley1064]

Hello,

I am working on a project that sends signals via 38khz modulated IR
remote. I see some circuits that use a 555, but it seems very error
prone due to tolerances, and I don't have anything to test for
frequency. I found this chip
http://www.rentron.com/remote_control/TX-IR.htm which is a programmed
PIC that does exactly what I want for $6.00 plus $1.50 for resonator.
Are there any other options, or should I not worry and use a 555,
possible with a trimmer.
Thanks
BB

Several manufacturers make series resonant crystals at exactly that frequency.
Digi-Key sells the Epson C-2 38.0000KA-P as their P/N SE3314-ND for $1.35 USD.
That, a couple of small caps, and a spare gate or two and you'll be good to go
at a guaranteed 100 ppm tolerance.

Good luck.
Chris

 

[robert a moeser]

Hello,
I am working on a project that sends signals via 38khz modulated IR
remote. I see some circuits that use a 555, but it seems very error
prone due to tolerances, and I don't have anything to test for
frequency. I found this chip
http://www.rentron.com/remote_control/TX-IR.htm which is a programmed
PIC that does exactly what I want for $6.00 plus $1.50 for resonator.
Are there any other options, or should I not worry and use a 555,
possible with a trimmer.

i would not use a 555. ever.

go for the rentron parts, unless your goal is to learn about building
oscillators. the cost is entirely reasonable.

i think the apps shown in the rentron datasheet are a bit optimistic -
if you use those schematics do not deviate from their design.

in particular regular serial comms over IR can be a bit dicey - you want
to look into how to format packets with some error detection and so
forth. googling here is a good place to start.

but the TX-IR will do exactly what it says, i bet.

if you get interested (or sick of paying $6 a pop) you can program a PIC
yourself. it's a long road, perhaps, but a relatively bump-free and very
much travelled one.

-- rob

 

[Bob Business]

Previously I was just going to connect the trigger to a transistor, to
turn on the leds. How would I do this with a crystal?

 

[Robert Monsen]

Bob, to drive the crystal, you need a driver circuit, which generally
consists of an inverter IC, a couple of small caps, and a couple of
resistors. Here is one that I've used:

4049A 4049B

|\ |\
+-| >O--+--| >O- Drive LED
| |/ | |/
| |
| 10M |
|-/\/\/-+
| |
| .-.
| | |R=100k
| | |
| _ '-'
| | | |
+-|| ||-+ 38kHz crystal
| |_| |
--- ---
22pF --- --- 22pF
| |
| |
+---+---+
|
===
GND
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