40khz Crystal Oscillator?

[dabnis]

In the other thread the discussion turned to MilesTag and PIC programming. I didn't want to cause confusion, so I started this thread.

I have been experimenting with ways to generate 40khz for a laser tag gun. The first way I tried, using a 555 timer, works. (I would still have to tie this to another 555 to conrol pulse length. For now it just sends continuously as long as the button is held.)

The next circuit I tried involved a 4060 binary counter, resonator, resistor and a couple of capacitors. When I transmit the signal, all I get is a bit of static/crackle from the piezo tied to the 40khz receiver.

Circuit is here: **broken link removed**

I'm pretty sure I have it right, but there is a bit of question about how I hook the IR LED into it: Currently I have anode/+ in pin 7 (40khz) of the 4060 and cathode/- going to battery negative. Also am I right in having pin 8 going into ground/battery negative?

I've read that people have good results with circuits using crystals (lots of lasertag guns apparently use them), and that the circuits use less parts and less power.

I'm looking for something I can tie into a 555 timer, to control pulse length, rate of fire, etc.

One crystal circuit that I've found so far is on that same link (scroll up one). I have a 74C14 and the other required parts, EXCEPT for the crystal. Anyone know of a good part # for Mouser or Digikey for a 40khz crystal? When I search the site, I'm overwhelmed with options.

Also, how would I hook it up so that it's using only gate 1 of the 74C14?

Sorry for all the newbie questions, but I really want to try a few different 40khz oscillators to find out which one is the best for this application.

Thanks!

 

[kchriste]

I'm pretty sure I have it right, but there is a bit of question about how I hook the IR LED into it: Currently I have anode/+ in pin 7 (40khz) of the 4060 and cathode/- going to battery negative. Also am I right in having pin 8 going into ground/battery negative?

Yes, pin 8 of the 4060 goes to battery negative. You need to buffer pin 7 of the 4060 with a transistor and resistors to get more power into the IR led if the range isn't enough for you. You should always use a current limiting resistor on a LED, however the 4060s output has limited current capability so no harm was done.

Anyone know of a good part # for Mouser or Digikey for a 40khz crystal? When I search the site, I'm overwhelmed with options.

Just go to Digikey and type crystal. Then select crystals under the heading "Crystals and Oscillators" then select 40Khz from the list and click "Apply Filters":
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=852333;keywords=crystal
Choose "Through Hole" as the "Mounting type". Surface mount ones are no good for noobs.

Also, how would I hook it up so that it's using only gate 1 of the 74C14?

Look at the datasheet:
http://www.datasheets.org.uk/pdf/466481.pdf
And you'll see that gate1 is on pins 1 & 2 of the 74C14.

 

[dabnis]

I understand about the current-limiting resistors. Even though these IR LEDs would be pulsed for brief moments, I'd like to have a resistor in line once I start pumping more current through (was only using 3v on the test circuit).

I would have pictured buffering being done with capacitors. I have much to learn! Would a 2N2222 transistor work for what you describe? I have some on hand. If so, which pin on the transistor goes to pin 7 of the 4060, and which pin goes to the LED?

Thanks again!

 

[audioguru]

The output current of a CD4060 is nearly nothing when its supply is only 3V.
A 2N2222 will amplify it when its base goes to pin 7 of the CD4060, its emitter goes to ground and the LED in series with a current-limiting resistor goes between its collector and the positive supply voltage.

 

[dabnis]

Excellent - thanks so much!