how to test TSOP 1738

[manju_gowda]

Hi all,
i tried to test TSOP 1738 using connection as shown in attachment but i didnt get output voltage. can anyone help me to solve this

 

[ronsimpson]

I can't find a TSOP 1738. What is the manufacture's part number?

 

[audioguru]

The datasheet for the TSOP1738 shows a filter capacitor connected between pin 1 and 2. The datasheet explains that the 38kHz IR must be modulated on and off in bursts with certain gaps between the bursts so that the AGC can reduce the gain to avoid interference from compact fluorescent light bulbs that produce continuous 38kHz IR.
Here is the datasheet:

 

[Nigel Goodwin]

As AG says, it's ESSENTIAL to have a decoupling capacitor from pin 1 to pin 2, a 47uF or similar will be fine - keeps leads as short as possible, poor layout (and no capacitor) will make it unstable.

I would also suggest a pullup resistor from output to +5V, as per my tutorial hardware:



You also need a scope to check it, a multimeter is no use - connect a scope to the output and point an IR remote control at the TSOP, when you press a button you should see the modulation signal.

 

[manju_gowda]

i tested as per the circuit given in datasheet but i didn't get any modulated signal, even i used pull up resistor also

 

[Nigel Goodwin]

i tested as per the circuit given in datasheet but i didn't get any modulated signal, even i used pull up resistor also

Did you use a scope?, and an IR remote for the signal? - the TSOP's are really VERY, VERY easy to use.

 

[dr pepper]

You can use a logic probe if you dont have a 'scope.
I have had instability issues with this device, I've salvaged a few and they usually have a 100r resistor and large electro filtering the supply to them.
Use a tv remote to test the device, one that you know works.
You can do a quick test on a tv remote by looking at it with the cam on your mobile, most of them are sensistive to infra red.

 

[audioguru]

A TSOP1738 works at 38kHz. A problem testing it with a TV remote is that the remote might work on a different frequency like 56kHz then the sensitivity of the TSOP1738 will be very low.

 

[Mosaic]

As it happens I am about to build a 'people counter' (another thread) using this TSOP.
https://www.farnell.com/datasheets/1809228.pdf
with a TSAL6100 pair of emitters.

I should start the physical build tonite or tomorrow. I'll be able to advise on how it goes for the OP.

I am running a 39.2Khz PWM, 50% DC as the common anode carrier (8Mhz PIC clk, I could OSCTUNE for exactly 38Khz) and I am using a 500 uSec interrupt to alternate (50% DC) IR emitter pulse bursts from 2 PIC pins by pulling to ground. I am going direct from the PIC pins to the IR emitters so I will have to current limit @ under 25mA. If the range isn't sufficient I'll have to add transistor drives for more TX current. I need about 3' range.

Nigel: I see your tut page mentions a IR driver transistor. What is the current pulse that you use?

 

[Nigel Goodwin]

As it happens I am about to build a 'people counter' (another thread) using this TSOP.
https://www.farnell.com/datasheets/1809228.pdf
with a TSAL6100 pair of emitters.

I should start the physical build tonite or tomorrow. I'll be able to advise on how it goes for the OP.

I am running a 39.2Khz PWM, 50% DC as the common anode carrier (8Mhz PIC clk, I could OSCTUNE for exactly 38Khz) and I am using a 500 uSec interrupt to alternate (50% DC) IR emitter pulse bursts from 2 PIC pins by pulling to ground. I am going direct from the PIC pins to the IR emitters so I will have to current limit @ under 25mA. If the range isn't sufficient I'll have to add transistor drives for more TX current. I need about 3' range.

Nigel: I see your tut page mentions a IR driver transistor. What is the current pulse that you use?

About 1A, normal for IR remote controls - giving 10m plus range.

However, as always, I fail to see why you would want to use the PWM hardware? - it's easier, more versatile, and more accurate to do it in software.

 

[Wade Hassler]

Tearing apart handheld remotes often reveals a 455 KHz ceramic resonator used as the clock for a small microprocessor: 455/12 = 37.91 KHz.
Using 455KHz as your clock would make a lot of the calculating drop out of the program, as well as lower the power drastically.

Not that I've done it.

 

[dr pepper]

Timer 1 in pics works well with said 455 kc resonator.

 

[Mosaic]

Well I got the TSOp working etc. BUT the AGC makes it very hard to calibrate a reflective trigger for objects passing by the TX & RX. Gotta get a TSOP without the AGC I guess.

 

[Nigel Goodwin]

Well I got the TSOp working etc. BUT the AGC makes it very hard to calibrate a reflective trigger for objects passing by the TX & RX. Gotta get a TSOP without the AGC I guess.

They don't make them without, what would be the point?.

 

[audioguru]

The TSOP IR receiver ICs are used for remote control inside a home where there are probably some compact fluorescent light bulbs continuously producing 38kHz IR. They are not used for detecting passing objects.
You can make your own simple photo sensor circuit with a photo-transistor and an opamp.

 

[Mosaic]

I was was going with page 2's advice on this:
**broken link removed**

 

[audioguru]

The new TSSP IR receiver ICs are not the old TSOP remote control ICs. They do not require the 38kHz to be modulated with bursts then will have interference from visible light, heat and other IR systems.

 

[Mosaic]

I don't think that's right. It does have a bandpass.
**broken link removed**

 

[audioguru]

The bandpass of 38kHz (other frequencies are available) IR receiver ICs is centered at 38kHz and the circuit is most sensitive at 38kHz. The bandpass is not very narrow so they still have some sensitivity at other frequencies and can receive interference from them.

The new TSSP IR receiver ICs reduce their sensitivity to visible light but can receive interference from it. Sunlight has lots of strong IR which can overload their photo-diode. Compact fluorescent light bulbs produce lots of 38kHz IR which can also overload them.

But the old TSOP receiver ICs have AGC which reduces interference.

 

[Mosaic]

Yes that's so. I am recoding the detection to work off an opposing reflector so the system expects an IR signal by default and detects blockages.