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Radio Shack Photo transistor

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  • Radio Shack Photo transistor

    Hi Everyone,

    Does anyone have suggestions for a compatible photo transistor to the Radio Shack one, 276-145. Can't find them anywhere in my area and their web site has none.

    I'm looking to build a timing gantry and I only have two of the Radio Shack brand and would like to match them up or go with another compatible one.

    Thank you,

  • #2
    Jameco 373001 looks similar.


    • #3
      Hello Bruce,

      What are you using for emitters?

      The reason I ask, I use the same Radio Shack 276-145 IR phototransistor with the RS 276-143 940nm IR emitter as my detector and source and this combination has been functional.

      Your choice in a IR detector should be determined by the wavelengh of your IR emitter.

      I purchased several of the Jameco 2129385 phototransistors to use with my Radio Shack emitter's and none of them would work. I was able to trigger the phototransistors with ambient light or a flashlight, they just did not like the wavelenght of the RS 276-143 emitter. I purchased several of the Jameco 112176, (T1 , 3mm dia, 940nm phototransistor) and all of the devices trigger just fine from my light bridge with the RS276-143.

      The reason I chose the 2129385 the first round was it was listed as 860/940nm and was 5mm diameter which would have fit my existing setup as a backup. When that did not work, I purchased the 112176 which is 3mm diameter , 940nm. I am willing to adapt the diameter if the device works.

      match up the wavelengths.

      Last edited by mike SoCal; 07-18-2017, 07:19 PM.


      • #4
        I had been using the same 276-145 phototransistors, until Radio Shacks dried up in my area. For the past couple of years I've been using the following from Jameco:

        Part no.: 2129385
        Manufacturer: Jameco Valuepro
        Manufacturer no.: UT1893-45-0125-R
        RoHS Compliant
        Data Sheet (current) [230 KB ]

        Catalog 171 , page 23

        They've been working fine as direct replacements, no issues. I don't use Radio Shack's emitters, I've used fluorescent under cabinet lights, as well as under cabinet LED's, and it's been working fine. Also SIGNIFICANTLY cheaper, you can get about 5 of these for the price of one 276-145, even cheaper when you buy 10 or more.


        • #5
          Thank you both for your feedback. My desire is to build a track timing system and the best information I've found on the subject is on Gregory Braun's HO site. I thought I'd follow in those steps and realized Radio Shack parts were not available. So as far, as an emitter, I'm not sure yet. I do have a couple of Radio Shack combo packs (emitter/ptransistor) but not enough for a 4 lane set up. So was thinking of then doing an overhead gantry with florescent lights. So as you can tell, I'm new to this timing project and would welcome and further guidance and suggestions. Thank you!


          • #6
            If you have the emitters and detectors that Radio Shack packaged together those do not match very well and are only likely to work if they are very close together. Here is a quote from an old post that I was able to dig up:
            "I have always found the photo-transistors and IR emitters from Radio Shack to be problematic. Their emitters vary in quality and as such, don't always trigger laps effectively. I have also seen their photo-transistors fail over time, probably due to using emitters with the wrong frequency. I have used matched components from DigiKey with much success: RPT-37PB3F for the photo-transistor and SIR-34ST3F for the IR emitter. If you read the spec sheet for the photo-transistor you are using, it should tell you which emitter to use."
            Last edited by RichD; 08-04-2017, 06:14 AM.


            • #7
              RichD is correct. The frequency of the light emitted by the LED is critical. The Trackmate and Slotrack sensors are sensitive to light having a wavelength of 850nm (Nanometers). If I remember correctly the RS LEDs operate at a frequency of 950nm. Infrared LEDs are typically available in 850nm or 950nm.

              While the 950nm LEDS can be made to work typically they have to be run at or near their maximum rating to trigger the sensors. The 850nm LEDs can be run at or below their nominal rating with success. As an example I made a bridge using 950nm LEDs. The LEDs in this bridge had to be run at their maximum rating (100mA) to be successful. The bridge had to be located within a few inches of the sensors. With 850nm LEDs the bridge could operate at less than 15ma and a maximum distance in excess of a foot!

              LEDs have a life expectancy that is dependent on how they are operated. When operated at or below their nominal current ratings an LED can have a life in excess of 50,000 hours. When operated at their maximum ratings that life is significantly reduced. As an example my first light bridges were made using 950nm LEDs and had a life of 3-5 years. I expect the a bridge using 850nm LEDs to have a life expectancy in excess of 15 years.