Jump to content
Sign in to follow this  

Simple Sensor

Recommended Posts

I want to measure the frequancy of a IR beam interrupted by a spinning fan blade.

I am usieing an MSP430G2553 


Here is a link to the sensor circuit.      http://www.dickbrom.com/circuits/dark.jpg


The voltage across the Red Led varies from 1.0 volts to 2.0 volts depending on the beam being interrupted or not. 


Can I connect the emitter of the 2n2222 directly to an analog input pin and the battery minus to the launchpad ground pin? 


There are a few Energia programs that show hot to compute the frequency. 




Share this post

Link to post
Share on other sites



You can do this, you won't damage your MSP, but it will not work I think because generally in digital ICs, logic 0 has a short range (something like GND <-> 0,8V) and it's a logic 1 above. So if your signal don't have a "clean" 0V state, you may miss some "shots".


Usually, open drain circuit are choosen in this case :



The signal is captured on the collector of the transistor. Advantages : you can use the voltage of the

Share this post

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

  • Create New...