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

B

Jan 1, 1970
0
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

C

#### CFoley1064

Jan 1, 1970
0
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 R #### robert a moeser Jan 1, 1970 0 Bob said: 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

B

Jan 1, 1970
0
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?

R

#### Robert Monsen

Jan 1, 1970
0
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
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

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