IR Sensor Hookup

[jrdamien]

I'm at my wits end with this again. Have been using a very reliable reed switch but want to use an IR sensor instead.

Here are the sensor and counter sheets.

http://www.vishay.com/docs/83760/tcrt5000.pdf
SESTOS

Anyone care to tell me how to wire that sensor to the counter? I've tried every which way but am obviously missing something. I'm using the counters onboard 12v supple and am using 47ohm resisters to drop the voltage.

[Joe Gwinn]

The datashhet of the counter is a bit ragged, but here is a starting point:

Connect counter pin 5 to opto sensor pins C and E. (This is the common ground.)

Connect counter pin 1 to sensor pin C. Configure sensor to Contact (NPN) mode. (This is the count pulse path.)

Connect counter pin 4 (+12 Vdc) to sensor pin A via a 1,000 ohm quarter-watt resistor. (This lights the LED in the opto sensor.)


Diagnosis: (Voltmeter required.)

There should be about one volt between sensor pins A and C, this being the voltage drop in the LED at around 10 milliamps. This voltage is constant. If some other voltage is seen, the LED may be defective. Hooking the LED up backwards may well destroy it. In this case, replace the sensor.

The voltage between sensor pins C and E should go up and down as the bobbin is rotated by hand. There will be low voltage (below 2 volts) when the IR beam from the LED is reaching the transistor via the reflector, and high (above 4 volts) when the beam is not reaching the transistor. If the voltage does not dip below 2 volts and rise above 4.5 volts as the bobbin turns, the counter will not count.

[jrdamien]

The datashhet of the counter is a bit ragged, but here is a starting point:

Connect counter pin 5 to opto sensor pins C and E. (This is the common ground.)

Connect counter pin 1 to sensor pin C. Configure sensor to Contact (NPN) mode. (This is the count pulse path.)

Connect counter pin 4 (+12 Vdc) to sensor pin A via a 1,000 ohm quarter-watt resistor. (This lights the LED in the opto sensor.)


Diagnosis: (Voltmeter required.)

There should be about one volt between sensor pins A and C, this being the voltage drop in the LED at around 10 milliamps. This voltage is constant. If some other voltage is seen, the LED may be defective. Hooking the LED up backwards may well destroy it. In this case, replace the sensor.

The voltage between sensor pins C and E should go up and down as the bobbin is rotated by hand. There will be low voltage (below 2 volts) when the IR beam from the LED is reaching the transistor via the reflector, and high (above 4 volts) when the beam is not reaching the transistor. If the voltage does not dip below 2 volts and rise above 4.5 volts as the bobbin turns, the counter will not count.

Thanks Joe. This was, unfortunately, how I had it hooked up. I was getting the correct voltage drop but was getting no voltage from between C & E. I had a pack of these sensors from three or more years ago. I doubt they were all bad but two days of trying to make them work is more than enough time.

I went ahead and bought these, instead:

https://www.sparkfun.com/products/9299
https://www.sparkfun.com/products/9322

[Joe Gwinn]

Thanks Joe. This was, unfortunately, how I had it hooked up. I was getting the correct voltage drop but was getting no voltage from between C & E. I had a pack of these sensors from three or more years ago. I doubt they were all bad but two days of trying to make them work is more than enough time.

I would figure out if the sensors are in fact broken before doing anything else, or the same problem may bedevil your next approach.

Testing a sensor is easy enough to do with a 9-volt battery, a 1000 ohm resistor for the LED and a 10000 ohm resistor for the transistor collector (pin C), a voltmeter, and a retroreflector or mirror.

Alignment of the mirror is critical. Retroreflector tape is far less critical, but cannot be too close to the sensor.

Note that the transistor in the sensor does not generate voltage. The point about configuring the counter to "contact closure (NPN) was to ensure that the counter would provide the needed sensing current to the transistor. Alternately, one can add a 10,000 ohm resistor from counter pin 4 to sensor pin C to provide the sensing current.