Wireless Assembly

How to build an IOT Hotdog.

Parts list

Custom Parts

3D Print

• Top Casing

• Bottom Casing

Order PCBs

Estimated Cost : 10 - 20 US$ per PCB

• Front PCB

• Back PCB

Specifications:

• Solder Mask : Yes
• Thickness : 1.6mm
• Layers: 2
• Size : 100 x 50 mm
• HASL : Yes

Stock Parts

• A1 : Arduino Nano or compatible + two 1x15 pin female headers

• BT1 : AAA battery holder (thru-hole mount recommended)

• C1 : 10 - 100uF capacitor (optional)

• C2 : ~1000uF capacitor (optional)

• D1-D3 : three white LEDs, I used 334-15 / T1C1-4WYA

• 12cm long hook-up wire connecting J1 to J4

• 12cm long hook-up wire connecting J2 to J3

• R1-R5 : five GL5528 photoresistors

• R6 : 1kΩ resistor (or lower if you're using less bright LEDs)

• SW1 : SPDT switch

• U1 : nRF24L01 + a 2x4 pin female header

• U2 : 0.8 - 5V to 5V boost converter + a 1x3 pin female header

• A transparent sleeve, I used This one.

• Mini zip ties

• Rubber bands

Programming

Arduino Nano

Extract this Zip file and upload
the file hotdog-fw.ino.hex to
the Nano using XLoader.

Windows

By default you should be able to
use COM0, if not try other ports.

Other

Nano-compatible microcontrollers

Compile & upload the Firmware using the Arduino IDE.

Dependencies

• Protothreads
• BTLE
• RF24

Assembly

Soldering Font PCB

1. Place the 1x15 headers on the Nano.

   I didn't have 1x15, so I cheated and yanked
   out one of the terminals from a 1x16.

   Don't be like me.

   

   
   

2. Solder the micro-controller to the PCB with
   its USB connector facing towards the edge.

   

   
   

3. Solder the photo-resistors to R1-R5
   on the opposite side of the PCB.

   

   
   

   It is recommended to clip the leads off
   before soldering to minimize heat loss.

   I prefer to also bend the wires in before clipping
   them short, so the parts won't come loose.

   

   
   

4. Solder the 2x4 header to U1.

   

   
   

5. Put the 1x3 female header on the
   boost converter and solder it to U2.

   Make sure V1 and V0 are aligned
   with the markings on the PCB.

   

   
   

6. Solder a capacitor of about 1000uF to C2.

   Mind the polarity.

   

   
   

7. Solder the SPDT switch to SW1.

   The terminals should go into the three holes in the middle.

   Mine was a bit over-sized, but as they
   say, if there's a hole, there's a way.

   

   Words to live by indeed.

   
   

8. If you have a thru-hole mount 1xAAA battery
   holder, you can go ahead and solder it to BT1
   and skip to step 13.

   Mind the polarity

   If you're using a cheaper battery holder like
   I did, we need to take a few extra steps.

   This can get quite messy though, so in
   retrospect I absolutely recommend
   getting a proper thru-hole mount.

   
   

9. First, trim both wires to about 2cm, and put some
   deep scratches into the bottom with a sharp object.

   This is crucial to ensure proper adhesion
   to the board, so carve it up like a psycho.

   

   
   

10. Then solder it to BT1 in the correct polarity.

    

    
    

11. Clean both the BT1 footprint and the
    battery holder with isopropyl alcohol.

12. Glue the battery holder to BT1 with epoxy.

    ⚠ Make sure there is at least 5mm clearance
    between the battery holder and the edge of
    the motherboard.

    It doesn't have to be precisely on the footprint,
    but do not place it any further below that.

    

    Clamp it down and wait for the glue to dry.

    Meanwhile, you can start assembling the Back PCB.

    
    

13. Solder a 100uF capacitor to C1.

    Mind the polarity.

    

    
    

14. Insert the nRF24 into the U1 socket,
    and that's the front motherboard done.

    

Soldering Back PCB

1. Solder the LEDs to D1-D3.

   Pay attention to polarity; one of the sides
   on each LED is flattened, line that up with
   the drawing on the PCB.

   

   
   

2. Solder a 1K resistor to R6.

   

   
   

3. Connect J1 to J4 and J2 to J3
   with 12cm long hook-up wires.

   Solder those in as well.

   

   The motherboards are now complete.

   

Final Assembly

1. Slide the PCB into the casing:

   Front PCB  ➞  Top Casing

   Bottom PCB  ➞  Bottom Casing

   Make sure the LEDs and the photo-resistors
   all face inwards, where the sleeve will be.

2. Secure each PCB with a zip tie and
   the cut-off end of another zip tie.

3. Add the sleeve.

4. Use zip ties to bind the two casing
   parts at their open ends together.

   Fasten the zip ties just tight enough that
   the casing won't separate from the sleeve.

5. Secure the other end of the casing
   to the sleeve with rubber bands.

6. Insert the battery, power it on and serve.

Operation

In wireless mode, the Hotdog is powered by a single
AAA battery that should last you about 2 - 3 hours
on a single charge.

I recommend using a rechargeable one.

There's no battery level indicator, so recharge frequently.

I'm still working on the client app for
wireless, but it's already looking great.

Stay tuned!