IEEE SouthEastCON 1999
Hardware Design Contest

Infrared Break-Beam Circuits

1. Infrared Emitter Circuit
   1. Emitter Parts List
   2. Emitter Conctruction
2. Receiver Circuit
   1. Receiver Parts List
   2. Receiver Conctruction

Infrared Emitter Circuit

Figure 1.0:Infrared Emitter

Figure 1.0 shows the schematic of the infrared emitter used for the break beams on the track. There are six emitters located at various positions on the track. Figure 2 shows the locations of the six emitters.

Figure 2.0: Locations of Emitter/Receivers on the track

The emitters are shown in red and the receivers are shown in blue. The emitter labeled number 4 is located at the top of the ramp. It's the only one not on the same level as the others.

The emitter card consists of one 555 timer configured to oscillate at 40Khz, two 74LS244 line drivers, six ten ohm resistors, and six male plugs. The 555 timer oscillates at 40Khz and the output is connected to the input of the first buffer on each 74LS244 chip. The first buffer drives three other buffers on each chip. In other words, each 74LS244 chip has three outputs that are connected to the male plugs on the card. The male plugs are just two pins from a single row header. One pin on the male plug is connected to the output of the 74LS244. The second pin is connected to a 10-ohm resistor. The other side of the 10-ohm resistor is connected to ground. Two 74LS244 chips are needed because one is not sufficient to drive all six of the emitters simultaneously. The emitter card draws approximately 300ma of current from a 5-volt supply. Table 1.0 shows a complete part list needed to construct two emitter cards. The parts were ordered from Jameco Electronics ( 1-800-831-4242 ) and Radioshack.

Constructing the Emitter Circuit

Place all of the sockets on the perforated board from Radioshack as shown in figure 3 first. Solder the first pin and the pin diagonal to the first pin on the other side of the socket. This will ensure that all of the sockets are stationary on the board. Break the 36 pin single row header in half and place the side with the longest pins down on the wire wrap side of the board. Take the other half of the header and place it three holes up from the other one. The top header should be ground and the bottom header should be 5 volts. Place the negative side of the 47uf radial electrolytic capacitor on the ground terminal and the positive side on the power terminal of the card. Place two 0.1uf capacitors in series to obtain the 0.05uf capacitor for the 555 timer. The resistors and capacitors for the 555 timer can be placed directly onto the perforated board and wire/soldered on the other side. The two 20 pin wire wrap sockets will hold the 74LS244 line drivers and the 14 pin socket will hold the six 10 ohm resistors needed for the diodes. Wire the circuit according to figure 1.0. After wiring the circuit, place 0.1uf capacitors across the power and ground pins of both 74LS244 chips.

Figure 3.0: Socket Placement Diagram

The final step in assembling the emitter card is to make the emitters. The high output infrared diode from radioshack has a long lead and a short lead. Take the 24 ga alarm wire from radio shack and solder the gray wire to the long lead and the white wire to the short lead. Next, take two of the 8 pin single female headers from Jameco and cut them into six pieces. Each piece should be able to accept two pins from the male plugs on the card. Select the appropriate length of wire needed and cut the wire. Solder the white and gray ends to the metal tabs extending from the female header previously cut. The emitters should be ready to plug into the card now. The white wire should be connected to the top pin of the male plug and the gray wire should be connected the bottom pin of the male plug. Repeat this five times for the rest of the emitters.

Receiver Circuit

Figure 4.0 Infrared Receiver Circuit Schematic

The receiver card consists of three LF347 quad opamps, six sixteen pin sockets, six fourteen pin sockets, and one 74LS04. One LF347 operates two receivers. The sixteen pin and fourteen pin sockets hold the passive elements the receiver needs. Table 2.0 shows a complete parts list for constructing two receiver cards.

Construction of the Receiver Card

First, place the 16 pin and 14 pin sockets on the perforated board from Radioshack as shown in figure 5.0. Apply a small dab of solder to the first pin and opposite pin diagonal to the first pin. This will hold the sockets firmly on the perforated board. The LF347 chip fits into the socket immediately to the left of the 16 pin sockets on the top and middle rows of the card. The 16 pin sockets contain 2 pin male plugs, an npn bipolar junction transistor, a 50 ohm resistor, a 470pf capacitor, a 10 ohm resistor, a 1Mohm resistor, and 1kohm resistor. The 14 pin socket below the 16 pin socket contains a 4.7kohm resistor, general purpose diode, 1uf tantalum capacitor, and a 1kohm resistor.

Take one of the 36 pin single row male headers and cut it into 12 individual pieces. Each piece should have two pins in it. Place the shorter pins on pins 1 and 2 of the 16 pin socket. Take the npn BJT and place it in pins 16, 15, and 14 of the 16 pin socket. Next, place the 50 ohm resistor in pins 4 and 13. Place the 470pf ceramic disc capacitor in pins 5 and 12. Next, place the 10 ohm resistor in pins 6 and 11. Place the 1Mohm resistor in pins 7 and 10. Place the 1kohm resistor in pins 8 and 9.

For the 14 pin socket below the 16 pin socket, place a 4.7kohm resistor in pins 1 and 14. Next, place the anode of the general purpose diode in pins 2 and 13. Next, put the 1uf tantalum capacitor in pins 3 and 12. Finally, put a 1kohm resistor in pins 4 and 11.

Wire the LF347, npn transistor, and passive elements as shown in the receiver circuit diagram in figure 4.0. . This basic setup should be repeated six times, once for each receiver.

The outputs of each of the rectifier diodes should be applied to the individual inputs of the 74LS04 chip. The outputs from the 74LS04 will yield a logic 1 when the break beams are broken on the track.

The NPN phototransistors from Digi-key ( LT1031 ) have a dark case for filtering ambient light. Place a piece of shrink wrap over the end to narrow the beam reception angle. This allows for more precise placement of the breakbeams and will cut down on false detection. Mounting the receivers on the board is easy. Take the gray and white 24 ga alarm wire from Radioshack and solder the white wire on the long lead of the detector. Solder the gray wire on the short lead of the detector. Next, cut one of the 36 pin single row male header into 12 individual pieces. Each piece should have two pins on it. Take the shorter side and wire the alarm wire to it. The longer sides go into pins 1 and 2 of the 16 pin sockets. They simply should plug in after routing the wire.

written by Robert E. Puckett

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