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Good idea. I never thought of using a 555. Do you know what value resistors and capacitor i would need to get the right frequency? Ive been using a 555 calculator and ive got 0.820K, 1.5K and 0.01uF. They give about 37.6MHz. Does it have to be exactly 38.5KHz?
Is there a way to calculate what resistors and capacitors to use? It would be better if there was a calculator where you can enter the Hz and it will calculate those for you.
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http://www.national.com/ds/LM/LM555.pdfOriginally Posted by The Master
The formula is in this data sheet near the end, page 10 between figure 13 & figure 14.
Last edited by Archangel; - 27th July 2009 at 07:14.
If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
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Sorry, i dont understand that formula. Its a bit more complicated than i thought.
Ive been reading a few webpages (and re-reading this thread) and i think im starting to understand how it works. I like the 555 idea but if i need to send it in bursts then ill need 2 555s (1 for the 38.5khz frequency and 1 to control the bursts). Other sites also recommend a variable resistor for fine tuning.
I think its best if i do use the PIC chip. I do still have the MCLR pin which can be used as an input only (for a sensor). Hopefully one of the pins on this chip has hardware PWM and hopefully that works how i think it does. That way i can adjust the frequency to suit and have the burst thing without having to make the PCB bigger and use extra components... and i wouldnt have to figure that equation out
Im going to put an order in soon and get some new emitters/PTs and ill see how it goes. No doubt ill be back for more help when it doesnt work :P
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Any of the PICs output pins can control the 555, look at the trigger pin of the 555. It is basically an on and off pin. The basic stamp folks did it this way before they had a freqout command.
Dave
Always wear safety glasses while programming.
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Thats a good idea. Ill add some 555s and the related components to my next order
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A simple beam break sensor, what about a $5.00 US laser module and a simple CdS cell ?
http://www.doctronics.co.uk/555.htm#transducer
easier formula here http://www.doctronics.co.uk/pdf_files/555an.pdf
Last edited by Archangel; - 29th July 2009 at 09:09.
If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
.
Gold is the money of kings, silver is the money of gentlemen, barter is the money of peasants - but debt is the money of slaves
.
There simply is no "Happy Spam" If you do it you will disappear from this forum.
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I dont want people to be able to see the beam but if i cant get IR working then that might be the only option.
Thanks for the links. Ill have a read through them
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