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Building F4GOH DRA818 APRS Tracker - M0YNG.uk

Created 2020-10-02

Modified 2021-02-10

Tagged

Amateur Radio
Construction
APRS

What is it?

TL;DR - a small low cost APRS tracker, which uses an arduino and a radio module.

Recently I was handed two kits with the understanding that if I could get both working, I could keep one.

F4GOH's blog post[1] has more info, but not quite enough to make it easy to just pick up and build.

1: https://hamprojects.wordpress.com/2015/07/01/afsk-dra818-aprs-tracker/

I have one working, now I'm going to make the other, and document the process to help anyone else do the same.

Parts List

*NOTE:** there are multiple versions, my PCB is marked with V1.2 and does have C8 and R7

The PCB looks like this

Green PCB with F4GOH written on it [IMG]

Underside of Green PCB with F4GOH written on it [IMG]

This is taken from the "Bill of Materials" for V2, from the zip file "DRAPRSV2", from F4GOH DRAPRS repo on github[2], but I've added the extra bits that my PCB has too.

2: https://github.com/f4goh/DRAPRS

Resistors (all surface mount)

2 R1,R6 1K
2 R2,R4 1.8K
2 R3,R5 3.3K
2 R10,R11 4.7k
4 R7, R12-R14 10k
2 R15,R16 330

Capacitors

6 C1,C2,C5-C8 100nF (surface mount)
1 C3 1uF
1 C4 100uF

Integrated Circuits

1 U1 DRA818 (surface mount)
1 U2 ARDUINO NANO

Transistors

1 Q1 2N7002 (surface mount)

Diodes

1 D1 1N4007 (surface mount)
1 D2 LED3MM (surface mount)

Miscellaneous

1 L3 VK200 (Inductor - the bits of wire in a black thing)
1 RV1 10K (potentiometer)
1 J3 BNC/SMA (for connecting aerial)
2 J1,J6 CONN-SIL10 (to join split boards)
2 J4,J9 CONN-SIL4 (for connecting OLED screen and GPS)
2 J7,J8 CONN-SIL6 (for the optional SD Card and other "accessories")
1 J5 ALIM (for 5v power to the board)
Several standoffs / screws
1 J2 CONN-SIL2 (Jumper to set output power. If present 0.2w, else 1w)
16 PT1-PT8,PT10-PT17 ENTRETOISE (Probably the through hole mounting points?)
1 PT9 GND (??)

Let's get soldering!

I have split this PCB in two, but you don't have to. I will refer to the arduino board (right half) and the TRX board (left half).

Surface Mount Capacitors

All the surface mount capacitors are the same, so let's start there.

C1 and C2 are on the top of the TRX board
C5, C6, C7, C8 are on the underside of the arduino board

PCB with capacitors highlighted [IMG]

Surface Mount Resistors

R1 and R6 are 1K (`1001`) one is by C2 on TRX board and one by the LED on arduino board
R2, R4 are 1.8K (`1801`) both are on the TRX board bottom and top
R3 and R5 are 3.3k (`3301`) both are on the TRX board, close to R2 and R4
R10 and R11 are 4.7k (`4701`) both are on the underside of the arduino board
R7, R12, R13, R14 are 10k (`1002`) all are on the underside of the arduino board
R15 and R16 are 330 (`3300`) and are together on the underside of the arduino board

underside arduino PCB with resistors highlighted [IMG]

TRX PCB with resistors highlighted [IMG]

arduino PCB with resistors highlighted [IMG]

Surface mount diodes

D1 is on the bottom on the TRX board, on mine the lettering is the "right way up" if it's oriented correctly
D2 is on the right side of the arduino board, on mine the green end of the LED is down

Surface mount Transistors

Q1 is on the TRX board

TRX PCB with diode and transistor highlighted [IMG]

Through Hole Capacitors

Now we're onto the easy bits!

C3 is 1uF and on the top of the TRX board, the negative leg is on the outside edge (note: I installed mine on the other side and folded over to help reduce height)
C4 is 100uF and on the arduino board

Miscellaneous

I'm leaving the ICs for last...

L3 is an inductor, bottom left of the TRX board (note: I also installed this on the back side)
RV1 is a potentiometer, on the arduino board
J3 is the aerial connector on the top of the TRX board (note: also back side)
J1 is the 10 pin thing to join the split boards, it needs to go on the under side of the TRX board, but only if you have split it
J6 is the other side of that 10 pin thing, it goes on the underside of the arduino board

Arduino Time!

Now is a good point to add the arduino, before any other headers are added around it to make life difficult.

I wanted everything to be as low profile as possible, so I soldered my arduino directly onto the headers. Be sure you want this, and maybe test the arduino first, before you do it!

Arduino PCB with arduino and other components fitted [IMG]

More Miscellaneous

J4 and J9 are 4 pin headers, both on the arduino board, one by the capacitor and one on the right
J7 and J8 are 6 pin headers, both on the arduino board, next to J4 and J9 (I didn't do J7)
J5 is the screw terminal thing, top of the arduino board

I don't plan to use the SD or low power, so left those headers off

DRA818

This is the main bit, the radio module.

A little tricky to get in position, because it's so big AND surface mount. Hold it in place with tweezers and solder one corner pin, then the opposite, and hope it's straight!

It's ok if the top three pins on the left connect to the shield, as they are all ground, but probably best to avoid? The bottom left pin is power, so DO NOT connect that to the shield.

TRX PCB with module fitted [IMG]

Quick Tests

Some quick tests, look for continuity between:

The bottom pin of the TRX board and the bottom left side pin of the DRA818
The top pin of the TRX board and anything that should be grounded, e.g. DRA818 shield, SMA outer.
VCC terminal on the arduino board and the bottom pin of J8, VIN on the arduino
GND terminal on the arduino board and anything that should be grounded, e.g. gnd on the arduino, headers, etc.

Put your multimeter in diode test mode, and it should light the LED with positive on the top, but it will be very dim

Stacking the boards

This is fairly simple, but some tips:

The TRX board needs to be flipped, the DRA818 should be exposed on the underside with the arduino on the top
If you are using standoffs, put some on the bottom too so it can stand off the floor
If you put anything on the middle (like me) it may need insulating from the underside of the arduino board (I used some spare foam from the screen's packing)
Metal connectors will help carry GND, but plastic also work

Stacked PCBs viewed from the top [IMG]

Stacked PCBs viewed from the bottom [IMG]

GPS and Screen

In most cases, the wires of these won't match the PCB nicely, so you will need to make up a wiring harness thing.

GPS

I have **VK2828U7G5LF** and only the middle four wires are needed. I won't give colours because they seem to change...

Counting from the left:

1. E - not used

2. G - Ground, goes to left pin on PCB

3. R - RX on GPS, goes to TX on the PCB

4. T - TX on GPS, goes to RX on the PCB

5. V - Volts in, goes to the remaining pin on the PCB

6. B - PPS signal, not used

Remember to put the heat shrink on before soldering stuff together!

Stacked PCBs with GPS modules connected in foreground [IMG]

OLED Screen

For me this was easier because I didn't have to solder wires...

From the top of the arduino board:

1. GND - GND on screen

2. VDD on screen

3. SDA on screen

4. SCK on screen

Build Done!

At this point the hardware is done!

I'm not going to cover connecting power etc. as that is entirely up to you, and there are many ways it can be done.

Next time I'll talk about software.

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