View Full Version : Detection of obstacles by infrared

01-03-2007, 10:39 AM
I have to detect an wooden obstacle placed at a distance of 5 to 12 cm from my robot. I have made a circuit using 555 timer as astable multivibrator with Ra=1K, Rb=18k and C=0.001microfarad to generate a frequency of 38KHz for ir ked and tsop1738 as ir receiver. But still I failed to get a desired output. Please help me with an working circuit diagram.Please also tell me about the placement of ir led and detector for the detection.

01-03-2007, 02:41 PM
Have you read the Data sheets??
Tsop's dont work with continuous signals!

01-03-2007, 03:12 PM
Also, with 555 timers always check on oscilloscope the frequency you are getting.

Most probably, the designed frequency won't match with the actual frequency. Use a pot to adjust the frequency to 38k and then use the required resistor (use less tolerance components).

Better still use a microcontroller (if possible) to generate the frequency. Will help with the bursts as well.

01-03-2007, 08:30 PM
Dear docel

Please explain me what is the meaning of continuous signals.I mean how do I get "burst" signals(what is the circuit) I do not know much about the working of the tsop. And please give me a diagram of an working circuit to try my hands on.

01-05-2007, 11:01 AM

I got some Vishay TSOP1738 and some Chinese made cheaper versions of the TSOP. While the Vishay module seems to need the "burst"s, the Chinese versions respond fine to a continuous 38kHz square wave. I decided to go with the Chinese ones as
* They are cheaper
* It is easier to generate a continuous square wave rather then a wave with bursts

Yes I do realise that I am rendering myself susceptible to interference from some lighting sources and sunlight :( . It is a trade off.


01-05-2007, 11:47 AM

I have a further question. Given that the TSOP does not respond to continuous signals, Why do a lot of people design TSOP based proximity detectors where the emitter is driven using a 555 based Oscillator ?

I took one such (http://www.electronic-circuits-diagrams.com/alarmsimages/19.gif) circuit and tried to use it with a TSOP. The TSOP responds, but immediately goes back to dormant state. It is then that I actually read the data sheets ( :oops: ) and realised that I needed to generate bursts.

What is the rationale behind using a 555 based osc to drive the TX ?


01-05-2007, 11:08 PM

01-06-2007, 10:15 AM
The other discussion is from 2005! I should do more thorough searching before posting. Thanks King.

01-06-2007, 08:21 PM
Thats agood question Arcane, and thanks Pratap for remembering that post :D

Now, all data Specs regarding the TSOP holds good ONLY for 17XX family by Vishay/ Telefunken and other European and American Modules. The Chinese modules are not Direct equivalents but "functional " equivalents only and do not share the TSOP17xx specs. There are numbers like HRM380017 and behave weird...
but - maybe they are desirable for the 555 non-burst scheme. :wink:

Another thing: The Circuit uses a BC107 NPN. This means the O/p is ON all the time until "IR detect" , remains on for some time till the base cap. discharges. The entire setup is for Pulse detection rather than any measurement or Data decoding (momentary). It is appropriate to use a PNP transistor for normal IR Detect= O/P ON.

08-01-2007, 10:13 AM

01-07-2008, 11:26 PM
I am working on a robot that detects a particular object upto 2-3m, and follows it.For this i need 'long range transmitter circuit and receiving sensors', be it ir or anything.
Where can I get such stuff from?
I am a newbie in robot-making and robotics india.Its the only forum where i can expect my queries to be answered by someone..