Infrared Activated Switch

[audioguru2]

i dont know if to use uF or F for C1. C2 it tells you to use uF. This confused me if whether to use uF also for C1.

The LM567 test circuit uses 0.0033uF (3.3nF) for C1, 0.005uF (5nF) for C2 and 0.02uF (20nF) for C3.

Im using a general design for the oscilator but ive drawn it anyway. When i change R2, Duty % changes. What does that tell me?

Your 555 circuit is conducting about 90mA through its IR LED which is plenty.
Of course the duty % changes because the cap is charged with 2 resistors but discharged with only one. This circuit will provide very close to 50% no matter what frequency it is adjusted: View attachment 37377

 

[hamoodyjamal]

Hi,

Seeing as there is no R1, what formula should i use to calculate the frequency?

And is this circuit garanteed to work? Because i've already soldered the components. But i can always desolder if it is going to work.

Regarding the LED, it is rated 100mA. so thats not a problem. Quite big considering most LED's are maxed at 30-40mA.

Thanks ;D

 

[audioguru2]

what formula should i use to calculate the frequency?

The calculation for R2 discharging the capacitor can be doubled, so would be 2 x (0.693RC), but since the output of a 555 doesn't go as high as +12V nor as low as ground then the frequency would actually be lower than calculated. You got a pot so just adjust it to the correct frequency.

is this circuit guaranteed to work?

Sure, with the cap discharged, the output goes high and the pot charges the cap. When the cap reaches the threshold voltage of pin 6, the output goes low and the pot discharges the cap until its voltage reaches the trigger voltage of pin 2.

I don't know the upper frequency limit of your phototransistor and I don't know how much ambient light you have which will saturate it.
I don't know which opamp you are going to use to see if it works at high frequencies. ;D

 

[hamoodyjamal]

Hi,

OK, i try the circuit.

Regarding the op-amp and the phototransistor, i'm willing to get a photodiode and any op-amp as long as they're available. I can try and get an SFH2030 or a General Purpose IR Photodiode from Maplin, and the op-amp from anywhere that i can.

SFH2030 - http://www.maplin.co.uk/module.aspx?ModuleNo=2242&doy=search
GP IR Photodiode - http://www.maplin.co.uk/Module.aspx?ModuleNo=2256&doy=24m7

What are you suggesting?

BTW, the NE567 is rated 0 - 500KHz.

Thanks ;D

 

[audioguru2]

Get the SFH2030F with the daylight filter. It has a much narrower pickup angle than the wide-angle Chinese one.
Get a TL072 dual low-noise opamp confiured as 2 stages with a gain of about 30 each.

Then you will have a home-made IR circuit similar to an IR receiver module without its important AGC. ;D

 

[hamoodyjamal]

Get a TL072 dual low-noise opamp confiured as 2 stages with a gain of about 30 each.

Sorry, im not quite following what you mean. Do you mean Amplifier-Amplifier, or Comprator-Amplifier or what?

Also, a gain of 30!? A transistor has more gain. Did you mean 30K?

Then you will have a home-made IR circuit similar to an IR receiver module without its important AGC

LOL, that sounds really cool!!! ;D

 

[audioguru2]

Sorry, im not quite following what you mean. Do you mean Amplifier-Amplifier, or Comparator-Amplifier or what?

Also, a gain of 30!? A transistor has more gain. Did you mean 30K?

A TL072 opamp has a voltage gain of 200,000 at DC and very low frequencies. Is frequency response is to 3MHz with a circuit gain of 1 and reduces to 1/10th for each increase in gain of 10. Therefore with a circuit gain of 100, its frequency response is to only 30kHz.

With a circuit gain of 30, its frequency response is to 100kHz.
With a gain of 30 from each of its two opamps in series, the total gain is 900 and its frequency response is to 50kHz. ;D

 

[hamoodyjamal]

Hi,

BTW, why do i need an op-amp in the first place? cant i just connect to the input of the NE567 to a photodiode? or is there not enough power?

Also, since the photodiode is a photo volatic cell, will it not give power to the input of the NE567?

The above 2 questions sound similar. But im not sure if the second one sounds right.

Thanks ;D

 

[audioguru2]

why do i need an op-amp in the first place? cant i just connect to the input of the NE567 to a photodiode?

IR radiation on a reverse-biased IR photodiode causes it to leak a tiny reverse-current. If you want a range more than a few cm then your circuit needs the gain of an opamp or two.
You could try an extremely high value for the resistor that feeds the IR photodiode its reverse voltage.
Then it would be slow (poor high frequency response) and might saturate from moonlight when it's cloudy at night. ;D

 

[hamoodyjamal]

Hi,

Is this circuit what i should be building?

Also, can you check if the op-amps and the photodiode (especially) are arranged correctly. If they're correct, ill just set my 555 timer to 100KHz.

BTW, my sister gave birth yesterday. So i might not get to the project very quickly. HEHE, im an uncle now!!! ;D ;D

Thanks ;D

View attachment 37382

 

[audioguru2]

Hi,
Congratulations, Uncle! ;D  I thought I was the uncle around here.

1) In your 1st opamp, you have a single supply, but it is drawn like it should have a dual-polarity supply. Pin3 doesn't have a reference voltage so will float around 0V. Then the opamp will amplify the difference in voltage of about 6V between its inputs 200,000 times and its output will be saturated near 0V.
2) Both opamps don't have negative feedback and are DC-coupled so will amplify (if the 1st opamp was biased correctly) mains interference from lamps and noise about 40 billion times and will probably oscillate with such a high gain.

I have re-done your photovoltaic circuit for you with the opamps biased at half-supply and using capacitor-coupling as highpass filters.
I prefer the photoconductive mode because it has additional highpass filtering.
You can try it each way if you want, I haven't built it. ;D

View attachment 37383

 

[audioguru2]

It looks like we are using the pin numbers of a single TL071 opamp instead of a dual opamp.
Check the datasheet for the correct pins.

 

[hamoodyjamal]

HEHE, silly me. I used the image of the 307 op-amp and just labeled it TL072. Sorry. :-[

I'll see to the project ASAP.

Thanks ;D

 

[hamoodyjamal]

Hi,

I changed the pin numbering accordingly. Is this better?

Also, are the "Inverting" and "Non-Inverting" Pins arranged correctly?

Tip: Pins 3 and 5 (+) are "Non-Inverting" and Pins 2 and 6 (-) are "Inverting".

Thanks ;D

View attachment 37388

 

[audioguru2]

HEHE, silly you again! ;D

Tip: You got it wrong, try this:

View attachment 37391

 

[hamoodyjamal]

Hi,

Im gonna be out of town for a week or so. Going to my sister, hehe, cant wait ;D

I wish i can get on with this headache project and just finish it.

Later!

 

[indra raharja]

Hi Audioguru,
now i have done my project with lm567 but it didn't work as i want. I use a LED as a load. But the LED still "ON" no matter the input frequency is out from my bandwidth setting. I've try a couple solution (like add a low pass filter) but it didn't change. I use a lm567 as a tone decoder from the frequency that i was send from FM transmitter (i was use ne555 as the information frequency). Can you give me any solution with this problem? thanks, and i hope your reply as soon as.

 

[audioguru2]

Hi Indra,
Welcome to our forum. ;D
Philips recommend a 0.01uF to 0.1uF ceramic disc capacitor directly across the power supply pins of their NE567 and an additional 10uF electrolytic cap if the supply has poor voltage regulation like from a battery. They also say to be careful with signal routing and to avoid ground loops.

Try disconnecting the input capacitor of the 567 from its driving stage and connecting the capacitor to ground instead to see if the LED turns off. If it does, then the problem is with the driving stage. ;D

 

[hamoodyjamal]

Im baaaack!

Wow, that took longet than i expected. Was fun though.

I see someone has built this project, or part of it. and is having some trouble. I couldn't quite understand what he/she wrote. Maybe you can shed some light on it?

I presume the cuircuit i should build works fine???? you know, the one with the TL072 and NE567.

;D