By Forrest M. Mims III
Has your TV remote control stopped working? Are you unsure whether the problem is with the TV or the remote unit? Well, you can quickly find out simply by pointing the remote control at this infrared remote control tester and pressing any button. If no buzz or tone is heard, it's time to replace the batteries or look for other problems.
How It WorksNear infrared pulses from a remote control transmitter are converted to a photocurrent by a silicon photodiode (PD) or even a silicon solar cell. C1 passes the pulsating signal to op amp LTC1050 while blocking sunlight (but not AC-powered household lights). The amplified signal from LTC1050 is passed to audio amplifier LM386 via C2 and trimmer pot R2, which serves as a volume control. The resultant signal from the remote controller is heard as a buzz or tone from the speaker.
Figure 1. Circuit for the infrared remote control tester.
Any silicon solar cell or photodiode can be used as the detector in this circuit. You can even use an infrared LED as the detector (see "Going Further.") The LTC1050 serves as a high gain preamplifier. The LM386 is an audio amplifier that drives a small speaker.
Parts You Will Need
The following parts were used to assemble a breadboard version of the circuit (Jameco part numbers in parentheses):
IC1 - LTC1050 op amp
IC2 - LM386 audio amp
R1 - 1M resistor
R2 - 10K trimmer pot
C1 - 0.01 µF capacitor @ 50V
C2 - 220 pF capacitor @ 50V
C3, C5 - 0.1 µF capacitor @ 50V
C4 - 100 µF capacitor @ 50V
PD - Silicon photodiode or similar
Speaker - 8Ω mini-speaker or similar
Perforated prototype board
9-volt battery, battery connector clip
Double-sided tape or 9-volt battery holder
Note: While the components listed above were used for the prototype, substitutions can be made. For example, many different silicon photodiodes or solar cells can be used for PD. Solar cells provide the longest detection range, but they cost more.
Prepare the Board and Install the ComponentsThe circuit was assembled on a solderless breadboard and tested. Once the circuit is operating properly, the components should be transferred to a 3.3 x 3.5 inch (8.5 x 9 cm) board cut from a perforated prototype board and soldered in place.
If you want to make a permanent version of the circuit, you can follow your own parts layout, you might also consider installing the circuit in a small enclosure. Or you can simply copy the layout I used shown in Fig. 2 to make a trial version of the circuit.
Figure 2. Layout for an assembled version of the TV remote control tester. The row and column index markers are on the back (foil) side of the board behind the margins.
You can follow the steps below to duplicate the prototype circuit shown in Fig. 2 or you can go on your own. Note that the circuit board holes given below are based on the column-row labels on the back side of the board. To simplify construction, you can mark labels for the key columns and rows on the upper side of the board.
1. The prototype board shown in Fig. 2 was cut along row 33 and the cut edge was filed smooth. This provides a board with an appropriate foil pattern on the back side for the parts layout shown in Fig. 2.
2. With the bottom edge of the board being row 32, insert the LTC1050 op amp into the top side of the board (without the foil pattern) so that pins 1 is in hole Q31 and pin 8 is in hole Q28. Bend pins 1 and 5 slightly outward to secure the IC in place.
3. Insert the LM386 amplifier into the top side of the board so that pin 1 is in hole Z31 and pin 8 is in hole Z28. Bend pins 1 and 5 slightly outward to secure the IC in place.
Figure 3. Annotated view of the components in the circuit.
4. Insert trimmer R2 in the board with its center pin at hole W28 as shown in Fig. 3. Bend the pins slightly outward to hold R2 in place.
5. Insert the leads of R1 into holes R32 and S27 as shown in Fig. 3.
6. Insert the leads of C1 into holes M32 and N32.
7. Insert the leads of C3 into holes S25 and V27.
8. Insert the leads of C4 into holes F25 and C27. Important: The minus (−) lead from C4 must go to hole F25.
9. Bend the lead from C1 at hole N32 to the lead from R1 at hole R32 and wrap the lead from C1 around the lead from R1. Use a low-wattage soldering iron with a well-tinned, small tip to solder the junction. Trim excess lead length.
Caution: Be sure to work in a well ventilated room when using lead solder.
Caution: Wear eye protection when using a wire cutter to trim leads and pins.
10. Bend the lead from R1 at hole S27 to the lead from C3 at S25 and wrap the lead from R1 around the lead from C3. Solder the junction and trim excess lead length.
11. Check to make sure all components are properly positioned and solder all the pins and leads of the above components in place. (C2, C5 and PD will be installed later.) Be careful to avoid applying too much solder.
12. Trim the remaining leads from C1, C3, C4 and R1 so that 1/4-inch (6 mm) or so remains for additional connections.
13. Cut a 1-1/2-inch (3.8 cm) length of solid hookup wire. Remove 1/4-inch (6 mm) insulation from one end and remove 3/8-inch (10 mm) insulation from the opposite end. Bend both exposed ends of the wire at a right angle to the insulated portion of the wire.
14. Insert the 3/8-inch exposed wire into the top side of the board at hole T32. Then bend the end of the wire up through hole S32, leaving a "U" shaped opening between the wire and the board. Later this opening will be used to connect additional wires.
15. Insert the 1/4-inch exposed wire into the top side of the board at hole C32. The wire should now resemble the green wire in Fig. 3. Flip the board over, and solder the wire at holes S32, T32 and C32. Trim only the wire emerging from the top side of the board at hole S32.
16. Remove 1/4-inch (6 mm) insulation from a 1.5-inch (4 cm) length of solid hookup wire. Insert the end of the wire into the top side of the board at holes A32 and X27. (Refer to Fig. 3 and see white wire between trimmer R2 and the 386 chip.) Solder the leads in place.
17. Remove 1/4-inch (6 mm) insulation from a 1.5-inch (4 cm) length of solid hookup wire. Insert the end of the wire into the top side of the board at holes B32 and W27. (Refer to Fig. 3 and see red wire between trimmer R2 and the 386 chip.) Solder the leads in place.
18. Remove 1/4-inch (6 mm) insulation from a 1.5-inch (4 cm) length of solid hookup wire. Insert the end of the wire into the top side of the board at holes B27 and R27. (Refer to Fig. 3 and see horizontal white wire between the LTC1050 and the 386.) Solder the leads in place.
19. Solder two wires to the speaker terminals. Wrapping wire works best due to its flexibility. One wire should be 2 inches (5 cm) and the second wire 1 inch (2.5 cm). Remove 1/4-inch (6 mm) of insulation from both ends of each wire.
20. Use a hobby knife to slightly enlarge hole E19 (at far right side of board) so that the two speaker leads will pass through it.
21. Slightly enlarge holes F4 so that it will receive a 2-52 screw. Attach the speaker to the board using a 2-52 screw and nut at this point.
22. Orient the speaker so that it is square with the edges of the board.and use a pencil to mark the second speaker hole between holes P20 and 21. Rotate the speaker out of the way and drill a hole at this point to receive a second 2-52 screw. Thread the two speaker wires through the enlarged hole E19. Attach the second speaker mounting hole to the board with a 2-32 screw and nut.
23. Solder the short speaker wire to the exposed negative (−) terminal from C4 at hole F25 (far right side of board).
24. Insert the end of the long speaker wire through the wire "U" between holes S32 and T32 (pins 3 and 4 of the LTC1050). Wrap the wire around the "U" at least twice. Do not solder it yet.
25. Use a hobby knife or small drill to form a 1/8-inch (3 mm) hole in the board at hole L22. This hole is for the leads from the battery connector. Check to make sure the wires will easily fit through the hole.
26. Insert the battery connector leads through the top side of the board and tie them into a knot on the foil side of the board. Leave at least 3 inches (75 mm) of wire on the top side of the board.
27. Flip the board over and trim the red and black leads to about 1 inch (2.5 cm). Carefully remove about 3/16 inch (5 mm) from the ends of the red and black battery clip leads.
28. Solder the red battery lead to the wire lead emerging from hole R27.
29. Insert the end of the black battery lead through the "U" between holes S32 and T32 (pins 3 and 4 of the LTC1050). Wrap the wire around the "U" Do not solder it yet.
30. Solder a short length of wrapping or other small gauge insulated wire between the holes at A32 and C32 (far right side of board).
31.Trim C5's leads to about 3/4 inch (2 cm) and form a small hook in the end of each. Solder one lead from C5 to the lead emerging from hole R27 (where the red battery lead is soldered).
32. Insert the hook in the remaining lead from C5 through the "U" between holes S32 and T32. Be sure the wires already inserted in the "U" are in place and solder them all in place.
33. Trim C2's leads to about 5/8" (16 mm) and form a small hook in the end of each. Place these hooks across R1 on the top side of the board and solder in place.
34. The final assembly step is to install the photodiode (PD). Insert its leads through holes G31 and H31. Bend the leads slightly outward to hold the photodiode in place.
35. Use wrapping wire to connect the PD anode pin to the "U" between holes S32 and T32 and solder in place.
36. Use wrapping wire to connect the PD cathode pin to C1's input lead at hole M32 and solder in place.
37. Put on some safety glasses and clip off all the excess wire lengths emerging from the back side of the circuit board.
38. Carefully check the circuit for any wiring errors or missing solder connections. Remove any solder bridges between foil traces using a solder sucker or braided solder remover.
39. When the circuit is completed, attach the battery to the board using double-sided tape or a 9-volt battery holder (see Parts List).
Testing the CircuitUse a small screwdriver to rotate R2's shaft to its center position. Press the battery connector clip onto the 9-volt battery terminals. The speaker should be quiet at this point. Point an infrared remote controller at the photodiode and press one of its control buttons. You should hear a buzz or tone from the speaker. If no sound is heard, remove the battery and carefully recheck your wiring. Incorrect wiring, a missing solder point or a solder splash between two foil traces might be the problem.
Adjust R2 for desirable volume. Keep in mind that higher volume settings will draw more current from the battery. If buzzing is heard when an IR remote controller is not activated, the circuit might be picking up the 60 Hz hum from a line powered light source. If the buzzing continues when the lights are out, disconnect the battery and check the wiring.
Going FurtherAs noted, a solar cell can be used instead of a standard photodiode to provide increased range. You can even use an LED as a detector, a principle I have described in various books and articles. Because LEDs detect a band of wavelengths that peaks slightly below the emitting wavelength of the LED, it's best to use a detector LED having the same or similar wavelength as the LED(s) in the remote controller. The vast majority of infrared remote controllers use 880 nm or 940 nm LEDs. If you don't know which yours uses, you might try connecting an 880 nm and 940 nm LED in parallel to form a dual-wavelength detector array.
About Forrest M. Mims III