Subject:
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Re: IR (formally 6.8nF cap)
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 13 Jul 2000 17:07:13 GMT
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Viewed:
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1031 times
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there's not really a big diff in the performance of the ir sensors
given 38 or 40 khz. so either is fine, +/- a few khz just doesn't
really matter, you have to detune 10 khz or so for it to matter.
there is an issue whereby there are two different varieties of hc132
chips, and depending on which kind you have, you need a very different
R value (or C, but R is easier to change).
here's more info:
*** re: R4's value. Depending on the variety of the manufacture of
the HC132 chip, R4 should be either 3.83K (Digikey 3.83KXBK-ND) or
6.81K (Digikey 6.81KXBK-ND). To test this, type "bit_set(0x1000,
0x40);" from the IC command line, and when the IR output circuit is
active (as evidenced by the IR OUT LED9 being on), measure the
frequency at pin 3 of the HC132. It should be 38 to 40 kHz. Use the
6.81K resistor to lower the frequency if it's too high; use the 3.83K
resistor to raise it if it's too low.
this info is avail in the latest parts list, at:
http://el.www.media.mit.edu/projects/handy-board/hardware/partlist.html
fred
In your message you said:
> I have asked for confirmation as to which frequency (38 or 40 KHz) is
> correct. As my current components should give me a frequency of 39KHz
> (1/3.883KOhm*6.6nF) I should be able to use either with out to much
> problem. I am thinking of using the output circuitry for the IR LED
> driver in conjunction with my hacked IR sensors which are rated for
> 40KHz so that I don't need to add extra circuitry. I am thinking of
> having the extra LEDs either chained in a serial or parallel
> configuration with the intended output LED (or maybe just replace it,
> however the LEDs for the sensors should realy be collimated for
> accuracy) and mounted with the associated sensor. Using the correct
> memory location I will turn the IR output on to produce the 39KHz
> carrier signal which the sensors should be able to use for distance
> measurement. Take the reading from the sensors (possibly multiplexing
> the values or maybe just feeding them into the analogue inputs) then
> turning the output off. Does this sound like a possible use ?.
>
> Thanks in advance for any help.
>
> John Hatton
>
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Message has 1 Reply:
 | | Re: IR (formally 6.8nF cap)
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| So as the 39KHz value would be ok for either the IS1U60 (38KHz) or the hacked sensors (40KHz), will my idea for the hacked IR sensor distance measurement using the IR output circuitry to drive multiple LEDs also be valid ?. Thanks for the help. John (...) (24 years ago, 14-Jul-00, to lugnet.robotics.handyboard)
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Message is in Reply To:
| | IR (formally 6.8nF cap)
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| I have asked for confirmation as to which frequency (38 or 40 KHz) is correct. As my current components should give me a frequency of 39KHz (1/3.883KOhm*6.6nF) I should be able to use either with out to much problem. I am thinking of using the (...) (24 years ago, 13-Jul-00, to lugnet.robotics.handyboard)
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