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Help desperately needed with PNA4601

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MrNobody

New Member
Recently I bought 1 PNA4601 IR receiver as well as 1 IR transmitter.
When I plug the IR transmitter and receiver onto Basic Stamp microcon and use the FreqOut command at 38500KHz, it works perfectly.. But them when I tried to construct a 555 timer circuit to send 38KHz through the IR transmitter, the PNA4601 receiver just cannot seem to detect the IR. I even put the transmitter soo close until both of the transmitter and receiver kissed each other and yet it doesn't want to work..

I have tried 2 different circuits with different components value for the 555 timer and both failed to work.

The first circuit I tried is found in IR_555Timer1.jpg attached below..
When I connect the output to the oscilloscope, it shows something like 70% duty cycle instead of 50%.

The second circuit I tried ia IR_555Timer2.jpg. The values for R1, R2 and C are 1K, 18K and 1nF respectively.. This time, when I connect the output to oscilloscope, it shows a 50% duty cycle. I even adjust the frequency to 38.5KHz with the potentiometer but it still refuse to work.

I have run out of ideas on how to make the IR work and am in desperate need of some help.. I have supplied continuous pulse of 38Khz and nothing seems to work.. Can somebody please help me..?
The purpose of the IR is for obstacle avoidance..

Thanks a million..
 

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Optikon

New Member
MrNobody said:
Recently I bought 1 PNA4601 IR receiver as well as 1 IR transmitter.
When I plug the IR transmitter and receiver onto Basic Stamp microcon and use the FreqOut command at 38500KHz, it works perfectly.. But them when I tried to construct a 555 timer circuit to send 38KHz through the IR transmitter, the PNA4601 receiver just cannot seem to detect the IR. I even put the transmitter soo close until both of the transmitter and receiver kissed each other and yet it doesn't want to work..

I have tried 2 different circuits with different components value for the 555 timer and both failed to work.

The first circuit I tried is found in IR_555Timer1.jpg attached below..
When I connect the output to the oscilloscope, it shows something like 70% duty cycle instead of 50%.

The second circuit I tried ia IR_555Timer2.jpg. The values for R1, R2 and C are 1K, 18K and 1nF respectively.. This time, when I connect the output to oscilloscope, it shows a 50% duty cycle. I even adjust the frequency to 38.5KHz with the potentiometer but it still refuse to work.

I have run out of ideas on how to make the IR work and am in desperate need of some help.. I have supplied continuous pulse of 38Khz and nothing seems to work.. Can somebody please help me..?
The purpose of the IR is for obstacle avoidance..

Thanks a million..

Some things to think about. Do you need 50% duty cycle? if not, then why didnt the one method work? Once you have verified that you can infact get a square wave working (555), make sure that the part you are using can source/sink enough current to fully illuminate the LED. I am not familiar with the basic stamp but output drive capability is one notable difference. Also, you can select resistor values to get you close to 50% duty cycle on the 555 circuit. I wouldnt worry bout that yet though. First make sure that you measure a good waveform on the output with the LED load. Maybe you killed the LED in the midst of fooling with it. DId you recently go back to the uC method to verify it still works?
 
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audioguru

Well-Known Member
Most Helpful Member
Mr. Nobody,
Did you use a powerful 555 IC or its weak Cmos sister?
If you used the powerful one then your first circuit has an IR current very low and the second circuit has the current even lower.

The ouput voltage of an ordinary 555 with a 5V supply goes up to only 3.8v and the 470 ohm resistor in series with the IR diode limits its current to only about 5mA. 50mA or more should be used.

A Cmos 555 is not able to drive an LED high when it has only 5V for a supply.
 

MrNobody

New Member
Thanks for all the reply...

Optikon:
I wasn't sure how to send the IR at 38KHz. I thought that I shuld send it at 50% duty cycle or somewhere around there.. Anyway, how should I send it...?
Yes, I constantly switch it back to Basic Stamp to test if it is still working and it is..

Norlin:
Thanks for the circuit..
Will test it out..

audioguru:
I am not sure what 555 timer it is because it is my friend's.. But when I measure the output voltage, it is around 5V and the current is around 50mA.
Btw, i replace the output resistor of IR_555Timer2.jpg with 220Ohm only.. When I put a normal LED instead of the IR, the LED lighted up..

Hope that info helps..
Thanks..
 
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audioguru

Well-Known Member
Most Helpful Member
MrNobody said:
I am not sure what 555 timer it is because it is my friend's.
Look at its part number. As shown in the attachment, An LMC555, TLC555 or Maxxxx is a Cmos 555 timer.

But when I measure the output voltage, it is around 5V and the current is around 50mA.
You showed a 5V supply and a 470 ohm resistor. The datasheet for a 555 shows a 1.4V loss when its output is high when the current is low and a 1.6V loss when the current is higher.
With the output at +3.6V, the LED is 1.5V and the resistor is 220 ohms then the current is only 9.5mA, not 50mA.
 

MrNobody

New Member
I think i know wats the problem...
Actually, nothing is really wrong with the circuit.. I think the minor problem is with the receiver.. The IR receiver that I am using only can only be triggered by sending a short burst of 38KHz unlike some sensor that can be triggered with continuous pulse of 38KHz..
I discovered that by accident while trying to remove the IR transmitter from the circuit while the power is on and putting it back (probably to change IR transmitter i guess).. Suddenly the receiver is triggered.. So I experiment by sending a PWM signal to the RESET pin of the 555 Timer and voila.. it works..

But another problem occurs.. the range is too short.. I will post the circuit soon to see what can be change to improve the range..

BTW.. the 555 timer I am using is NE555..
 

audioguru

Well-Known Member
Most Helpful Member
The NE555 is the original ordinary 555 that has up to 200mA output current.

Most IR receiver ICs have automatic-gain-control that reduces the gain when there is continuous 38kHz IR pulses from compact fluorescent lamps. The gain is max when bursts of data are received like from a TV's remote.
 

Roff

Well-Known Member
I haven't read this thread carefully, but I did notice you mentioned 38kHz and 38.5kHz. According to the datasheet, the PNA4601 is tuned to 36.7kHz. Also, you need a transmitter LED with 940nM output wavelength. Several other wavelengths seem to be available (e.g., 850nM) which are outside the sensitivity curve of the PNA4601
 
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audioguru

Well-Known Member
Most Helpful Member
MrNobody said:
How can I increase the distance of the IR..?
1) Tune the transmitter's 555 oscillator to the exact frequency of the IR receiver.
2) Transmit bursts of 16 pulses with a pause between bursts so that the AGC in the receiver doesn't reduce its gain.
 

MrNobody

New Member
Ron H said:
Also, you need a transmitter LED with 940nM output wavelength. Several other wavelengths seem to be available (e.g., 850nM) which are outside the sensitivity curve of the PNA4601
You mean there are different kinds of IR transmitter LED..? I thought they are all the same.. Oops... How to tell which LED emits which wavelength..? I couldn't even find a model number on the IR LED I have..


audioguru said:
1) Tune the transmitter's 555 oscillator to the exact frequency of the IR receiver.
2) Transmit bursts of 16 pulses with a pause between bursts so that the AGC in the receiver doesn't reduce its gain.
To tune the frequency of 555, I replace the R3 in the circuit with a 5K pot..?

As for generating 16 pulses in 400us, isn't that equavalent to 40KHz..? I mean, 400us/16=25us --> 1/25us=40KHz.. Will it still work even though the carrier frequency is 36.7KHz..?

If I need to have a pause between pulses, I may need external device say, a PIC to reset the timer..? But my intention was to make it a standalone IR transmitter circuit..
Another 555 timer to generate a square wave of 1.25KHz (1/800us) to the reset pin will do the trick i guess but is there any simpler/cheaper circuit that can do the same thing..? Maybe with simple components like Inductor, capacitor and resistor..?


Another question. If the pause between pulses is longer that 400us, will it affect its performance..?
 
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bananasiong

New Member
The frequency of the output of the 555 timer id determined by this.
For the duty cycle, (R1+R2)/(R1+2R2)
 

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audioguru

Well-Known Member
Most Helpful Member
MrNobody said:
You mean there are different kinds of IR transmitter LED..? I thought they are all the same.. Oops... How to tell which LED emits which wavelength..? I couldn't even find a model number on the IR LED I have.
Buy one that has spec's that match your IR receiver's 940nM wavelength.

To tune the frequency of 555, I replace the R3 in the circuit with a 5K pot..?
A 5k pot will tune very coarsly. Use a 1k pot in series with a 1.2k resistor.

As for generating 16 pulses in 400us, isn't that equavalent to 40KHz..? I mean, 400us/16=25us --> 1/25us=40KHz.. Will it still work even though the carrier frequency is 36.7KHz..?
16 pulses at 36.7kHz is 436us. 15 pulses is 409us. Either one is fine.

If I need to have a pause between pulses, I may need external device say, a PIC to reset the timer..? But my intention was to make it a standalone IR transmitter circuit..
Another 555 timer to generate a square wave of 1.25KHz (1/800us) to the reset pin will do the trick i guess but is there any simpler/cheaper circuit that can do the same thing..? Maybe with simple components like Inductor, capacitor and resistor..?
There are many simple square-wave oscillator circuits. Gate the 36.7khz oscillator instead of reseting it. When a 555 is reset then the first pulse is longer. Maybe a CD4060 oscillator/counter can be used with two diodes and a resistor making a gate. The diodes drive a transistor that blinks the IR LED.

If the pause between pulses is longer that 400us, will it affect its performance..?
Ask Panasonic. Their datasheet is a brief translation from Japanese. The details are missing in English.
 
One realy easy way to boost the range of your transmiter is to take something like a small tube and cover the ir LED to focus the ir energy as it's moving away from the transmiter. You can do this just by taking a peice of black construcktion paper roughly 2 inches long and 1 inch wide, and wrap it around something like a pencil and tape it so it doesn't unroll, then just slike it onto the LED (if it seems a littlle tight on the LED then you have done it properly and it will not come off very esily. You will howeve need to point the transmiter more directly at the receiver.

On the reciever end you can do something simalar (if you were using an ir phototransistor then it would be exactly the same as the ir LED). Since you are using a different kind of ir receiver, you can make a small black box around the ir receiver (remembering that you need to leave a small opening to allow ir to come in) you can cover the opening with some kind of plastic (ie:something from a cell phone package or old CD case) and cover it with a dark red sharpie. This will block stray light waves that may be entering the receiver and confusing it into thinking that is receiving a signal.
 
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