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infared break beam detector from forrest mims green book

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maverick8888

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i just built this circuit and i was hoping someone had built this circuit and had the voltages or know what could be wrong with mine. i traced it a million times and i cant seem to figure out whats wrong. can i force the relay to switch to make sure its still ok?

thanks for any help
 
I only see a Break Beam for a Model RR Crossing Flasher Lights and it is not IR. What Book are you in? I am in The Green Radio Shack Version Called Getting Started In Electronics by Forrest M. Mimms, III Cat#276-5003
 
green book

im in the Enginner's mini notebook volume one. It has projects on timers, op amps and optoelectronic circuits. i bought this one at fry's
pg 116
 
I don't have that one if you Post the circuit I may be able to help.
 
I think this is the schematic there talking about. I apologize for the hack job, but i didn't have my scanner hooked up to this pc so i used a digi cam and pasted the 2 pages together.
 

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vaineo, thats the one. thanks for posting that being i dont have a scanner. i built the project for a class project with other circuits built on top of it and it wouldnt work... but when i took the current from the collector straight to the trigger (pin 2) of the 555 it would detect the beam if there was an interruption. i bypassed the dual opamp entirely but didnt have enough curent to flip the relay. can i wire it the way it is now and take the detected signal (from collector of Q1) and THEN run it through the opamp stage to THEN have enough to flip the relay? or should the circuit work properly the way it is? i remember the thing that stuck out the most was the fact that the voltages at the output of the first half of the opamp was the same of the output of the second half, kinda weird. im glad the circuit is half way working, im relatively new so its cool just to see something. thanks all i do appreciate the help.
 
i havn't tryed building this one yet. When it was built properly was it the range that was actually causing it not to work or did the circuit physically not work at any distance?
 
no the circuit wasnt working... the led at the bottom stayed on continously stayed on like the beam was never on. i know i was throwing a signal out there and receiving one by measuring the current through the collector. the voltage was amped after the first amp and wouldnt amp on the second coming out of pin 7 on the 1458. would my idea mentioned above work? if i took the current to the trigger of the 555 and also took that same line and then took it to the opamps to get the line amped and then to the relay to flip the relay? or does the circuit only work the way it is?or has any one built a infared beam detector like this before and knows of one thats been built and works?
 
The two transistors on the left are oscillator that
pulses IR diode. Opamps are simply amplifier to
create stronger AC signal and increase range of the unit.
Q2 and 555 build monostable which controls the relay.
Take a look at this link for more detail on operation
**broken link removed**
I suspect fried 555 chip because there is no diode across
relay coil (anode to pin3, cathode to pin8 of 555 chip).
 
i really appreciate the explanation on the circuit. do you know where i can get the whole circuit explaned like that? thats the kind of stuff i want to know.... cause i can build labs for school but as far as looking at the circuit and disecting it ... i cant do that but i would like to know what the componets are used for. thanks again....
 
You book could have some explanations and this fourum is
not the worst place to start :) (unfortunatelly my time is limited,
I'll try to answer specific questions). Btw, I just looked at the drawing
again and I noticed the diode D1 to the right of relay coil. I didn't notice
it before because of way it's drawn.
There is one more thing I did't notice last time (always in a hurry...)
it's the R5 pot. As far as I remember pin7 of the 555 chip is open
collector output used for discharging of capacitor (it simply shorts it
to gnd). Problem is that if this happens while R5 is set to it's lowest
resistance, that transistor which is inside 555 would blow (and the Q2
transistr as well). I would add small "safety" resistor such as 1k in
series with the R5.
There is no current limiting resistor for IR diode either (sender) but
that might be ok since it should work with low duty cycle.
 
hotwaterwizard said:
Check out this circuit!]
...hi !!! i'm planning to build this circuit, can somebody tell me the exact name or number of this so called popular Sharp module? and how many inches can its beam reach?
thanks....
 
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