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# 555 timer - 1200hz square wave generator? Answered

I would like to replicate the Hitechnic IR Beacon.  Essentially, this means that I need to create a 1200hz square wave.  I would like to do this with a 555 timer, a 3v power source, and infrared LEDs (1 - 3).  Please offer any suggestions you might have.  This will work in conjunction with the Hitechnic IR Seeker and an NXT Bot that I will program in RobotC.
Thank you.

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## 8 Replies

Re-design (author)2010-01-10

Here is a good flasher circuit.  I don't know what the rate is.

Here is a good tutorial site that  will help you calculate the approx. frequency.  If you need it exactly 1200 then you will have to check it with a freq. meter.

frollard (author)2010-01-10

...and the frequency will fluctuate with temperature - based on the 555 timer's temperature and the parts used in the circuit.  It might work with a range of frequencies, but odds are it needs to be relatively precise.

What a person could use is a 32.whatever khz clock crystal - and a binary counter (frequency divider) - and an 8-input 1 output and gate to say "if all these bits of time are set, then it's been 1/1200th of a second; lastly a flipflop that is configured to pulse-on-pulse-off to make the full square wave.

Re-design (author)2010-01-11

If accuracy is needed then the clock crystal is a far better answer.

raykholo (author)2010-01-11

Thank you all.  Ultimately, I would like to keep this as simple as possible in the interest of time constraints, so I will not be using a microcontroller or crystal...In past experience with 555 circuits: +- 20seconds...   Also, I would like to use a CR123A battery I have (www.dealextreme.com/details.dx/sku.8683) as the power source - would it be safe to trickle charge this while it was still in the circuit? and a good, minimalistic trickle charger please?

As for the precision needed, I am currently looking at Xander Soldaat's driver to see if I can read a "general" IR signal, not limiting me to the 600hz or 1200hz that the sensor setup uses.  I know for a fact that a tv remote does work with the IR Seeker (as according to the robotc "NXT Devices" menu (allowing me to view sensor and motor rotation data).  It is just an API question then which I will solve when I have a minute.

Re-design (author)2010-01-11

The CR123A is not a rechargeable battery is it?  If it is not then no you can't trickle charge it or charge it otherwise.

raykholo (author)2010-01-12

this particular one actually is; as stated by writing on the battery itself and comments on that page.  Dealextreme is not the most credible source, but I believe that it is rechargeable.  I actually do not have a trickle charging circuit, hence the reason I was asking this question: if you could provide me with a schematic to a minimalistic design of such that would be much appreciated...

Today I was able to successfully breadboard an astable 555 emitting a ~600hz square wave - driving an IR led.  (RobotC provides support for the 1200hz signal and a 600hz also.  The perfboard design of this is in the works, to be completed within another day or so.

So I need a small trickle charger circuit.  I have some DC Jacks so maybe if I could do the power input from a wall-wart when charging...

Also I have seen some other similar threads in questions here so I might make an instructable about producing this...

Thanks for all of your help (frollard and Re-design), and again please help with the smallest possible trickle charger.  I will look around at some instructables to see what I can come up with.

Re-design (author)2010-01-12

Just google for a charger that will charge at 1/10 or below capacity and the would probably clasify as a trickle charger.

frollard (author)2010-01-11

Those lithiums are protected - which can mean a few things, short circuit protection, overvolt, or undervolt protection.  Ideally it has all of the above.

If you have the battery in the circuit and it receives more power than it has, then it will charge until full.  It should charge so long as more power is provided to the entire circuit than is being used by the rest of the circuit.  If you have a trickle source, why not just run the circuit off that source?