[SOLVED] TSOP 1738 gives vary output

[hirenn]

Hello !

i have TSOP738 and make simple test circuit like below,
i connect its PIN1 to GND, PIN 2 to +5v(using 7805) with 100 ohm resisot, PIN 3 to multi meter Red probe (to meausre DC volt) and Black probe to GND

when i ON the Power Supply i get variation output from 2.3v to 5v at PIN 3 of TSOP 1738..

i didnt use remote here or any IR transmitter..

can anybody please tell me exactly what happening here???

 

[Audioguru]

The datasheet for the TSOP1738 recommends a 4.7uF capacitor to ground at its pin 2.
The output is shown as the collector of an NPN transistor with a pullup 80k resistor to Vs so maybe your voltmeter has a resistance too low. They show an optional 10k pullup resistor.
Maybe you have a source of IR nearby.
Maybe your TSOP1738 is a fake or is defective.

 

[hirenn]

thanks for reply
so to get constant output , should i have to use 4.7 uF cap at pin 2 ???

 

[betwixt]

The capacitor is there to keep the impedance across the ground and VSS pins low. It improves stability and noise rejection.

From your description, the meter you are using is drawing current from the TSOP output pin and loading it. They are only rated to source very small currents so drawing even a small current from the pin will make the voltage drop. In normal use as a data output that isn't important but if you want to improve the current it can provide, add a 10K resistor between the output pin and VSS (as well as the capacitor!). To see the real voltage on the pin you have to use an oscilloscope or logic analyzer.

Brian.

 

[pranam77]

There are a lot fakes in the market for TSOP1738. Are you sure the device you have has been marked with the same exact name or SC0038? which is from china?

 

[hirenn]

Thanks pranam77
I have checked it...it's sc0038 not tsop1738
Now what should I do? What is ouput of sc0038

 

[pranam77]

Thatz the fake one available abundantly in Indian market which will never work as expected. Try to get TSOP1738 or TSOP1736 or TSOP1228 or HC0038 which will work fine. Try the exact component on online sites like
www.united77.com,
vegarobokits.com,
robikitsindia.com
onlinetps.com

 

[hirenn]

Thanks for kind reply,
i Have SM0038, can i use it instead TSOP1738 ??

 

[pranam77]

SM, SC series are fakes makes from china available for dirt cheap prices which never work or have problems later. Try getting the Original TSOP from reputed dealers. Finding the right dealer is a bit troublesome but the circuit will work for sure.