IR Transmitter circuit help

Thread Starter

Native34

Joined Mar 30, 2020
17
I've already invested to much time to quit now. All i'm trying to do is connect two wires together remotely. Unfortunately i'm no Electrical Engineer, so i am trying to learn more about electricity and circuits as i go. The input pin is connected to 5V with a 220 ohm resistor. Then when you touch the input wire to any grounded part of the mill it causes the pin to change state. The problem with getting this to work with the IR TX/RX circuits, has been getting the voltage to go below 3.0V and stay there until the machine moves back the other direction. When i press the button on the switch it activates the TX but only momentarily, So it just blinks the RX and not makes it stay on until released. I have tried several different circuits found online, with similar results. Some didn't have any results at all.

What worked the best so far is connecting the ground wire to the emitter of an NPN Transistor and the input pin to the Collector, then connecting the output of the TSOP4838 to the base. The problem with that is that i have to pull the resistor from the base to get the circuit to work then place it back in when i want to simulate the other direction. Something like the image below. The only difference is there is no R2, and R1 is 4.7K. The other problem is it never really sinks the voltage below a few volts from 5V to between 2-3.4V. I really need it to go as close to 0V as possible. Transmitter is similar to th e one below. The other thing i need to do is invert the switch for the trigger of the transmitter, as it is normally closed and the transmitter will only trigger on the down state of the switch not the up state.
1585767892299.png

1585767694368.png
 

hexreader

Joined Apr 16, 2011
567
I suspect that you need the dual-555 circuit, not the single 555 version. The dual version emulates TV remote more closely

Most IR remote control receiver chips cannot give a low out for a long period, even with a steady 38KHz input. (some can)

Check datasheet of your IR receiver for maximum length of mark signal.

(pedantic point, but arrow is pointing the wrong way for Q1. BC558 is NPN, not PNP) EDIT: I got this completely wrong - stupidly reading wrong datasheet - see AudioGuru post later which has it right):eek:
 
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hexreader

Joined Apr 16, 2011
567
If you happen to live in UK I might be able to put two TSOP4838 IR receivers (4.5V to 5.5V operation) in the post to you. These seem able to give a permanent low with steady 38KHz signal.

This goes against the spec given in Vishay data sheet, which hints at a maximum burst length of 70 cycles. Might do some experimenting....

No idea if they are suited or reliable enough for your application, but you can have them for free.

EDIT: - did a bit of experimenting, and my TSOP4838 receiver happily gives a low for steady 30% 38KHz IR transmission. Stayed low without a glitch for 5 minutes. 5V supply and receiver 10cm from IR transmitter LED. No idea what I was feeding Tx LED, other than 0 to 2V square wave 30%duty from 50 Ohm function generator. This is outside Spec, and your TSOP4838 may behave differently.
 
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Thread Starter

Native34

Joined Mar 30, 2020
17
I suspect that you need the dual-555 circuit, not the single 555 version. The dual version emulates TV remote more closely

Most IR remote control receiver chips cannot give a low out for a long period, even with a steady 38KHz input. (some can)

Check datasheet of your IR receiver for maximum length of mark signal.

(pedantic point, but arrow is pointing the wrong way for Q1. BC558 is NPN, not PNP)
Is a dual 555 timer a 556 timer? If so is it the same as using two 555 timers?
 

Thread Starter

Native34

Joined Mar 30, 2020
17
If you happen to live in UK I might be able to put two TSOP4838 IR receivers (4.5V to 5.5V operation) in the post to you. These seem able to give a permanent low with steady 38KHz signal.

This goes against the spec given in Vishay data sheet, which hints at a maximum burst length of 70 cycles. Might do some experimenting....

No idea if they are suited or reliable enough for your application, but you can have them for free.

EDIT: - did a bit of experimenting, and my TSOP4838 receiver happily gives a low for steady 30% 38KHz IR transmission. Stayed low without a glitch for 5 minutes. 5V supply and receiver 10cm from IR transmitter LED. No idea what I was feeding Tx LED, other than 0 to 2V square wave 30%duty from 50 Ohm function generator. This is outside Spec, and your TSOP4838 may behave differently.
I am using the TSOP4838 IR receiver I can't get it to stay high or low constantly. It will only go low momentarily. Do you have an example of how you had these circuits wired to get it to stay high or low steadily?
 

Thread Starter

Native34

Joined Mar 30, 2020
17
One of the other problems i am having with the receiver out pin, is that when i send a button press of the Transmitter it will only dip from about 5V to 4V. It will not go any lower. Does anyone have any insight into getting the output to drop to lower than 1V maybe around a few hundred mV from 5V?
 

hexreader

Joined Apr 16, 2011
567
I was thinking of two 555s, but yes, 556 is fully equivalent. Whichever is easiest for you to implement.

Sounds like you have a different TSOP4838 to me. I just struck lucky and happened to find some that behave differently to specification.
 

hexreader

Joined Apr 16, 2011
567
Are you measuring the 5V to 4V drop with a multimeter or an oscilloscope? A multimeter seeing a typical TV remote signal might well show 4V average for a 0 to 5V pulse train if average duty cycle is 20% at transmitter, causing 80% at receiver (which sounds about right for TV remote)

Note that any figures I give are all approximate - accuracy is poor, and highly unpredictable with IR communication
 
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Thread Starter

Native34

Joined Mar 30, 2020
17
hexreader, I'm using a multi-meter as i don't have an Oscope. I think part of th problem with the oscillation is i am using disk capacitors and i think i should be using electrolytic caps. So the circuit wasn't actually oscillating or modulating.
 

Audioguru again

Joined Oct 21, 2019
5,413
Your IR receiver circuit has the transistor in the wrong place and it is upside-down.
The IR receiver is designed to detect pulses of IR at the burst of pulses and with gaps between bursts as shown on the datasheet.
It is done that way so it does not detect the continuous 38kHz from a compact fluorescent light bulb, but your 555 circuit is producing 38kHz continuously without the important bursts of 38kHz with gaps between bursts.
 

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Bernard

Joined Aug 7, 2008
5,784
What range is required ?
What pointing accuracy is needed ?
I am thinking that a OPL 561-OC ( open collector ) sensor might work. Choose frequency up to 200k baud, no coding required.
several options available in OPL 5XX series.
Tx OP145 ,935 nm compatable.
 

Thread Starter

Native34

Joined Mar 30, 2020
17
What range is required ?
What pointing accuracy is needed ?
I am thinking that a OPL 561-OC ( open collector ) sensor might work. Choose frequency up to 200k baud, no coding required.
several options available in OPL 5XX series.
Tx OP145 ,935 nm compatable.
The range is under 10 ft. and mot sure what you mean by pointing accuracy, but I would like it to work in 360 degree rotation. Unfortunately IR is line of sight so i can live with that, just have to mark the tool with direction when i set it up.
 

Thread Starter

Native34

Joined Mar 30, 2020
17
One issue i'm having is that i can't seem to find an Electrolytic capacitor in the values of 1nF needed to make the circuit work at 38K. I have used the 555 calculator and all the values that they say work, i have not been able to find sources for. Also thank you guys for being generous with your knowledge.
 

Audioguru again

Joined Oct 21, 2019
5,413
Dodgy - would this circuit work with an ultrasonic transmitter in place of D1? Thinking of using it for a different application...
No. An ultrasonic transducer is piezo that draws no DC current like the LED does. Use an ordinary NE555 or LM555 instead of the low power TLC555.

One issue i'm having is that i can't seem to find an Electrolytic capacitor in the values of 1nF needed to make the circuit work at 38K. I have used the 555 calculator and all the values that they say work, i have not been able to find sources for.
Use a 1nF plastic-film capacitor. Electrolytic values are MUCH higher.
 

Thread Starter

Native34

Joined Mar 30, 2020
17
After doing some additional research on circuits i came across one of these little micro controller chip. Does anyone know if i can use one an Attiny85 micro-controller in place of the 555 timer to reproduce the modulated signal that the receiver is looking for using arduino code, and interface it with an IR Led to accomplish the same thing? I'm just thinking that i'd like to keep this circuit as compact as possible, and adding another 555 timer will take up some real estate that i don't have room for.
 
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