Help me solve a bug in txr of my robot

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electron_boy

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bug in my robot

hi everybody,
last month for an exhibition in our college i did my first bot which can sense any obstacles and can turn its path. for detecting obstacles i constructed a proximity sensor with ir txr and rxr(tsop1738)

i designed the txr with 555 astable for 38khz.but practically i got only around 25khz then i modified it putting a pot instead of 'Ra' and measured the frequency as 38khz but the theoretical value was aroun 50khz what would be probably wrong.
plz help

bye
 

bug in my robot

LM555 datasheet from National Semiconductor said:
The external capacitor charges through RA + RB and discharges through RB.
Click to expand...

The error is approximately 30%.

Error source could be:
1) Charging/Discharging capacitor
2) Internal ESR of Charging/Discharging capacitor
3) RB resistor
 

Re: bug in my robot

I wouldn't blame resistors unless you used something unknown, not for error of this sort..
The most probable reason will be the capacitor as caps quite often have +/-20% (or more) tolerance..
 

Re: bug in my robot

IanP said:
I wouldn't blame resistors unless you used something unknown, not for error of this sort..
The most probable reason will be the capacitor as caps quite often have +/-20% (or more) tolerance..
Click to expand...
I agree with you, IanP. The error due to RB and probably the ESR in the cap was compensated by the POT already. Should be the cap in this case.
 

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