TransponderBuild
This instruction will guide you through building a transponder to use in the car.
The PIC chip used in the transponder can be programmed with the decoder optional programmer hardware or Microchip tools.
The project can be built on perfboard. The critical part for manual assembly is winding the spiral antenna. The circuit itself is very simple.
This is the schematic for the transponder:
Cut a small piece of perfboard 7 holes * 11 holes (standard 0.1 inch). Notice in the image the two larger holes drilled for the servo wire.
Install the chip socket and solder the 5MHz crystal and the two capacitors C3 and C4. The chip is held in place by the solder on pins 2 and 3. Leave the other pin of C3 and C4 unsoldered.
Mount all the power supply components:
- the P Mosfet Q1 VP2106N3-G
- the low drop regulator U1 LP2950
- the two filter capacitors C1 and C2 - CHECK THE POLARITY
Leave the ground pins unconnected, and solder all the others. Pin 1 of the chip socket will be soldered as well. Leave unconnected the two input pins of Q1 as in the image:
Mount the LED and the limiting resistor R1. Use a piece of shinrk tube around R1 and led pins to avoid rubbing against the antenna wire. Align one terminal of the LED to the teriminals of capacitors C3 and C4. When bent, it will connect most of the ground points.
Mount the output resistors R2 and R3 and the two capacitors C5 and C6. Leave unsoldered the pins that go to the antenna, solder and cut all the other.
Connect the servo wire. Use a piece of shrink tube as an extra strain relief across the two enlarged holes. Bend and solder the wire, and connect all the ground points.
Solder 4 small pieces of wire in the four corners. Wrap 19 turns of 0.125 mm diameter enamel-insulated wire around the board. Clear the ends and solder to the output terminals of C5 and C6. Bend the corners on the outside. Program the PIC with the firmware and push it into the socket
You can wrap the transponder in rigid shrink plastic or in a small box. This is how it looks:
RCHourglass Project - Marco Venturini - mv4wd