First of all i want to say hello to everybody on this site.
Since i am new i hope you would take my mistakes in english language as a minor problems.
I am not so ¨green¨ at electronic but i am still learning and a think that people learn through their whole life. I know that there was an subject like this already on this site but i want to get it more clearly so every help is welcome.

I want to build an IR transmiter and an IR reciever that would work up to 10 m if i am not to much pretencious(anything between 5-10 m would be great). So i have 2 Cmos 555 timer (TLC 555 CP) and a TSOP 1730(for reciever) so my desirable frequency is 30 khz.It is crucial that operating voltage of transmiter circuit if possible is 3 V since it would be operated from a 2 AAA bateries-1,5 V.I have already start building up this circuit but max. distance i can reach is about 10 cm.I try to use both PNP and NPN,i try to change duty cycle(from 5% to 80%),i try to sink and source but the result is the same.First i want to clear all doubts with a transmiter circuit and later with a reciecever(although i think/know that reciever circuit is not so complicated)

So far let me introduce in things that i know and that i already been able to do:
-first IC(IC1) must operate on frequency of 30 kHZ(R1,R2 i C must be on the values that would acomplished desired frequency and possible higher values that would lower the current)-DONE
-second IC(IC2) must operate on frequency so it can create a burst of signal and his output must connect on a reset pin of IC 1-DONE
-Between power suply should be decoupling capacitor so it can deliver current to IR led in transmiter circuit and would expand battery life-DONE
-IR led diode should be picked for a desireble forward current(in my case desirable current is about 80ma and a diode forward current is 150 mA with a forward voltage of 1.2-1.6 V)-DONE
-Wave lenght(nm) of a diode and a TSOP 1730 must be equal-DONE
-TLC 555 or every 555 can operate as a sink or source curent. Preferable is to sink current because he is able to sink more rather than source-DONE
-for acomplished desirable curent transistor must be introduced to output pin 3 of a first IC(type of transistor depends on sinking or sourcing current)
-transistor must operate in the folowing conditions:since i think my circuit is better to operate as a sinking source in this case i will use a NPN type.It must go to saturation and that would be acomplished when Vce is aprox. 0 V and a Vbe is about 0.7 V(emiter is lower than base voltage).
So in the collector circuit i must drop all voltage on a diode and a resistor for a desirable current and calculate depending on hfe of a transistor base current(considering voltage drop on base resistor and Vbe).So the current collector-emiter would be curent of a base gained by hfe factor.Preferable chose slighly higher base curent for ensuring full saturation mode.

Things i am not sure of:
-since my duty cycle is aprox 60% does this means that on the output at pin 3 of the first IC should i measure 1.8 V??(because depending on what i connect to output pin 3 measuring are different)
-How IC 2 affect on the IC1 (is he lowering the frequency of IC 1 ??because when i measure frequency on IC 1 witouth conected to IC2 freq is 30 khz and when i conect IC2 to reset pin on IC1 i am geting 18 khz)???
-i am not sure how load on pin 3 afect on IC1 and why??
-should i increase/decrease duty cycle??
-loking at a NPN datashet electric characteristic testin voltage is 6v,mine is 3V.How to define hfe of transistor??

Every information about everything would be apreciated because i want to learn,unfortunately despite i finished my energetic school i live in such society that electronic is on another plan.
Attaching transmiter circuit.
NOTE: all resistors are variable , transistors that i have are NPN 2SC1740 ,PNP BC 328

 

[
optus said:
"Things i am not sure of:
-since my duty cycle is aprox 60% does this means that on the output at pin 3 of the first IC should i measure 1.8 V??(because depending on what i connect to output pin 3 measuring are different)"

Keith replied:
What are you measuring the voltage with and what are you connecting to the pin to make it change?

optus said:
"How IC 2 affect on the IC1 (is he lowering the frequency of IC 1 ??because when i measure frequency on IC 1 witouth conected to IC2 freq is 30 khz and when i conect IC2 to reset pin on IC1 i am geting 18 khz)???"

Keith replied:
What are you using to measure the frequency with? The frequency generated by IC2 is about 10 times slower than that generated by IC1. When the output of IC2 is high, IC1 will generate pulses. When the output of IC2 is low, it will hold the reset pin of IC1 low and stop it from running. The result is that IC1 is only generating pulses for about half the time. That is why the overall frequency appears to be about half what it is when the reset pin on IC1 is held high.

optus said:.
"-i am not sure how load on pin 3 afect on IC1 and why??"

Keith replied:
what are you loading it with and what is the effect?

optus said:
"-should i increase/decrease duty cycle??"

Keith replied:
For what reason?

optus said:
"-loking at a NPN datashet electric characteristic testin voltage is 6v,mine is 3V.How to define hfe of transistor??"

Keith replied:
If the circuit is working, why do you need this?

Regards,
Keith

 

[
optus said:
"Things i am not sure of:
-since my duty cycle is aprox 60% does this means that on the output at pin 3 of the first IC should i measure 1.8 V??(because depending on what i connect to output pin 3 measuring are different)"

Keith replied:
What are you measuring the voltage with and what are you connecting to the pin to make it change?

optus said:
"How IC 2 affect on the IC1 (is he lowering the frequency of IC 1 ??because when i measure frequency on IC 1 witouth conected to IC2 freq is 30 khz and when i conect IC2 to reset pin on IC1 i am geting 18 khz)???"

Keith replied:
What are you using to measure the frequency with? The frequency generated by IC2 is about 10 times slower than that generated by IC1. When the output of IC2 is high, IC1 will generate pulses. When the output of IC2 is low, it will hold the reset pin of IC1 low and stop it from running. The result is that IC1 is only generating pulses for about half the time. That is why the overall frequency appears to be about half what it is when the reset pin on IC1 is held high.

optus said:.
"-i am not sure how load on pin 3 afect on IC1 and why??"

Keith replied:
what are you loading it with and what is the effect?

optus said:
"-should i increase/decrease duty cycle??"

Keith replied:
For what reason?

optus said:
"-loking at a NPN datashet electric characteristic testin voltage is 6v,mine is 3V.How to define hfe of transistor??"

Keith replied:
If the circuit is working, why do you need this?

Regards,
Keith

First of all thank you very much for your reply.I apriciate that
All of my measure are done with uni t 81c handheld osciloscope.On the pin 3 i measured the voltage first witouth load,and then with transistor conected to it with ir led diode and resistor in colector region.
The problem is i do not getting desired gain(curent through ir led) and since datasheet of transistor said that at 6V hfe is min.120 i am not sure that my transistor even is saturated though i doubt since Vbe is around 0.45 V and Vce near 2 V??My suply is 3V.

 

hi optus,
Are the 555's CMOS or the 'regular' 555 versions.?
E

 

Hi Optus. Assuming your IR emitter is a 5mm LED, mount it in a plastic box using a rubber grommet. This made a big difference for an IR project I made years ago. I don't know why.

 

I would look into using an irDA receiver.
Most systems operate at 38kHz or 40kHz.

Modulating an IR LED is straight forward if you want to use MCU for transmitting and receiving.

 

hi optus,
Are the 555's CMOS or the 'regular' 555 versions.?
E

Thanks for reply.I apreciate that...
It is CMOS

Hi Optus. Assuming your IR emitter is a 5mm LED, mount it in a plastic box using a rubber grommet. This made a big difference for an IR project I made years ago. I don't know why.

Thank you for reply.I apreciate that.
I am afraid it take a bit more for increasing range or in other words i must increase a curent

I would look into using an irDA receiver.
Most systems operate at 38kHz or 40kHz.

Modulating an IR LED is straight forward if you want to use MCU for transmitting and receiving.

Thank you for reply.Apreciate it....
Since this is my first serius project i want to be straight forward starting from scratch...i want make an efort and deserve succes if at the end

 

hi optus,
I appreciate that you want to transmit IR over a distance of 5+ mtrs, what information, if any, how will the 38kHz pulses be encoded.
E

 

hi optus,
I appreciate that you want to transmit IR over a distance of 5+ mtrs, what information, if any, how will the 38kHz pulses be encoded.
E

The frequency is 30 kHz and already i am able to achieve that.Transmiter circuit is made of 2 cmos 555 timers and a reciever circuit is Tsop 1730.Problem is that the distance for now is to short and the curent through an ir led is to small.I want to explore and find out why.Is it problem with the transistor or something else...Data/signa is send through burst mode between two timers

 

Have you measured the frequency of your modulating oscillator (the second 555)

From a 555 calaculator I get 63 KHz. Way too high.

Each burst needs to be 10 cycles or more followed by 14 cycles or more of dead time.

That means the max frequency you can use to modulate it is 30K / 24 = 1.25 KHz.

I would lower the frequency to something like 500 Hz with close to 50% duty cycle.

I have used these, and indoors at least, it could be recognized anywhere in a room with the remote pointed in any direction. They are very sensitive when used properly.

Bob

 

h optus,
This is 5V powered Version I built some time ago, for driving a TSOP
E

 

Have you measured the frequency of your modulating oscillator (the second 555)

From a 555 calaculator I get 63 KHz. Way too high.

Each burst needs to be 10 cycles or more followed by 14 cycles or more of dead time.

That means the max frequency you can use to modulate it is 30K / 24 = 1.25 KHz.

I would lower the frequency to something like 500 Hz with close to 50% duty cycle.

I have used these, and indoors at least, it could be recognized anywhere in a room with the remote pointed in any direction. They are very sensitive when used properly.

Bob

Omg sorry about that.You are absolutly right.Now i can see that my capacitor value on IC2 is wrong.The real value is 1 micro F.so the frequency is somwhere at 600 Hz

h optus,
This is 5V powered Version I built some time ago, for driving a TSOP
E

Thank you...looks very nice

 

Omg sorry about that.You are absolutly right.Now i can see that my capacitor value on IC2 is wrong.The real value is 1 micro F.so the frequency is somwhere at 600 Hz

That's more like it!

Bob

 

The beam width of the transmitter LED should be narrow, +- 6 deg. would be nice. 30 mA to 50 mA should be ample. I had same sensitivity result as @BobTPH, no place to hide.
As last resort a short focus lens can extend range, and -or a reflective cone on receiver.

 

Can someone tell me if this is a good schematic? Because the main problem is that i cannot reach desired curent trough the ir led?? Witouth transistor pin 3 is on 1.7 V,with transistor pin 3 is on 1 V...
Note;IC2(right IC) C is egual 1 micro F not 10 nF

 

Because the main problem is that i cannot reach desired curent trough the ir led??

hi optus,
Consider this, you have a 3V supply, assume the IR diode has a Vfd of 0.8v, so that is 2.2V/7.5R = 290mA [ you are expecting]
Assume the transistor has a Gain of 10 at that Collector current, means 290mA/10 =29mA Base is required.

You have a 525R connected from 555 pin #3 to the Base, assume a 3V drive, less 0.7Vbe ie 2.3V / 525R = ~ 4mA !!!!Base current.

Look at the CMOS 555 d/s and check the Out pin #3 current source limit.

E

 

hi optus,
Consider this, you have a 3V supply, assume the IR diode has a Vfd of 0.8v, so that is 2.2V/7.5R = 290mA [ you are expecting]
Assume the transistor has a Gain of 10 at that Collector current, means 290mA/10 =29mA Base is required.

You have a 525R connected from 555 pin #3 to the Base, assume a 3V drive, less 0.7Vbe ie 2.3V / 525R = ~ 4mA !!!!Base current.

Look at the CMOS 555 d/s and check the Out pin #3 current source limit.

E
View attachment 189715

As i said before in this thread my suply is 3V,ir led forward voltage is 1.2 V and desired curent is 80 mA.From my point of view if duty cycle is 60% i cannot ever have 3V on the output of 555.In best case that should be 1.8
V.Because 0.6×3=1.8.Further more 1.8-1.2=0.6 V on colector emiter region.So 0.6/80 mA is 7.5 ohms.Calculating base curent is 1.8-0,75=1.05 V.To be ensure that my transistor is gona reach saturation region i must divide voltage with curent.I assumed that my hfe is 50 so 0.08/50=0.0016 A.I took a bit larger curent 0.002A so desired resistance is 1.05/0.002=525 ohms.is this ok?

 

hi,
The figures I posted where best case values.
Do this simple test, disconnect the 525R from pin #3 and temporarily connect to the +3Vsup, measure the IR LED DC current, post what you measure.
E

 

hi,
The figures I posted where best case values.
Do this simple test, disconnect the 525R from pin #3 and temporarily connect to the +3Vsup, measure the IR LED DC current, post what you measure.
E

Hi
I am aware of everything that you said but that does not give an answer to my guestion/s.The thing is very simple.I have 555 cmos timer with a duty cycle of 60%.My question is why i cannot get curent of 80 mA through colector of NPN transistor which base is conected to the pin 3 of 555 timer?If you can just look into my schematic that i posted earlier...i want to know if that schematic is valid.NOTE:capacitance on IC2 is 1 microF instead 10nF
Thank you

 

hi,
How are you measuring the current in the IR emitter.?
Did you try that test I suggested.?
E