Calgary Amateur Radio Association

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Blinking Lights TDOA RDF Antenna Project

This article is a detailed description of how to source and assemble a wonderful little project originally published by Dave NZ1J.   It takes a TDOA project documented on this site elsewhere to a new level.    The original TDOA, built with a 555 timer, is extremely easy to build, but only gives an audio indication of the direction of the fox.  

This project uses a PIC mcu and LED's to indicate the direction to the fox.  It requires a bit more hardware to construct, but with a group buy, we were able to source the PCB and parts for around $26 ea.  

See this video by Dave NZ1J of a demo ==>

Below is the schematic and some photos to help with your build.    
Note: that the electrolytic Capacitor C2 goes with the ground at the bottom, not according to the symbol, but rather the + sign on the top. 

The BOM (Bill of Materials) is the following:

Item QTY Part Digi-key Part Number References
1 1 PIC Pocessor PIC16F18324-I/P-ND U1
2 1 14 Pin Socket ED3114-ND U1
3 1 78L05 497-7268-ND U2
4 2 2N3904 2156-2N3904-FS-ND Q1, Q2
5 2 PIN Diode 568-1922-1-ND D1, D4
6 4 Green LED C503B-GCN-CY0C0792CT-ND D5, D6, D8, D9
7 1 Red LED C503B-RCN-CW0Z0AA1-ND D7
8 4 1k Resistor 1.0KQBK-ND R3, R6, R13, R17
9 8 4.7k Resistor 4.7KQBK-ND R2, R5, R10, R11, R12, R14, R15, R16
10 2 470k Resistor 470KQBK-ND R1, R4
11 1 220pF Cap 399-14053-1-ND C6
12 1 0.01uF Cap 399-9772-ND C5
13 3 0.1uF Cap 399-4264-ND C1, C3, C4
14 1 10uF Cap 493-17435-1-ND C2 (Note: align according to the + symbol up)
15 1 1uH Inductor 78F 1R0K-TR-RCCT-ND L1
16 1 Slide Switch 450301014042-ND SW1
17 1 9V Battery Clip 36-232-ND TP+

The files that were provided by Dave NZ1J to me so that we could get our own PCB's made and PIC chip programmed are available to our club members by contacting me by email at ve6pds @ this domain (

Also, Here is a blog posting:

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