Wednesday, November 9, 2016

Halloween Candy Cauldron V3.1

V3.1 in the enclosure. Ignore the external speaker--it's a vestige. Ready to tidy up for V4.
As I said in my last post on this project, all that was left to do was tidy up the connections and enclose the electronics. I decided that the enclosure I was using was too big. The reason it was too big was that I had the project on a breadboard instead of soldering the components to a PCB. I have always wondered why places like Radio Shack that sell enclosures and PCBs don't sell PCBs that fit in the enclosures--with mounting holes and screws.  So, I went looking and found this enclosure with matching PCB and a battery compartment. A little pricey, but good quality and they have a variety of sizes and features. (I'm using the term PCB to include proto boards here.) Follow-up note: I found that the soldering pads on the pcb were insufficient.  I'll accept blame for my soldering technique, but I had more trouble with this than any other I've worked with.

Since the new enclosure was a little smaller, I decided to use an  +Arduino Pro Mini (actually an Arducam clone) instead of the +Adafruit Industries Pro Trinket.  It's a little smaller, and I had a few in inventory. It needs an FTDI to serial module to program, but I was using one anyway for the Trinket to be able to use the serial monitor.

The code compiled with no changes.  (See link to last post in opening sentence to see code.) In order to upload to the board, the IDE required some changes (to point to the right board--Nano, not mini), and the USB Port needed a tweak in Windows Device Manager (I'm on Windows 10). Arduino.cc has a clear and concise getting started article describing this better than I can.

Interrupt

Note that the interrupt code also works as-is.  I need to work on the program to make the sleep more useful. As you can see in the video (the blue LED is on when it's sleeping), it doesn't sleep much, I'm using the Echo pin on the HC-SR04 sensor to wake it up. I put it to sleep at the top of the loop, then wait for Echo to go LOW or HIGH. It works the same either way, at least to the naked eye.

I used LOW because IDLE is the only mode that can be woken from anything other than LOW, and I wanted to be able to play with other modes. I'm thinking about using an inverter so I can set the interrupt on LOW, but have the pin go LOW when the Echo pin goes HIGH. +Home DIY Electronics has a good article on interrupts and the HC-SR04.

Since the sensor is ranging constantly, it wakes up pretty quickly. If I try to put it in power down mode, it does not wake up (maybe because the sensor shuts down?):  The LED indicating sleep stays on and no gesture will wake it up. There are 5 sleep modes and these are only the 2 extremes. I will play with some of the intermediate modes--next year, or the next time I'm playing with interrupts on an AVR board.

Construction
  1. Test the mini
    Since I changed boards, I needed to upload the code, wire the circuit on a breadboard, and test. As described above, all was well.
  2. Prep the enclosure
    In this design, the speaker and the battery are now inside the enclosure, I only need holes to bring in wires from the switch and from the HC-SR04. I also drilled 7 holes to let the sound out, places where I planned to put the speaker.
  3. Design the board layout
    I needed to mount the Pro Mini, then find room for the amplifier and Micro SD Reader.  This required some planning, so I simulated with header pins on the PCB and marked where I would place the components.  All the components had male headers attached, because I originally set set this up for a breadboard, so I soldered the headers to the printed side of the board.
  4. Wire the busses
    I created power and ground busses on the inside edge of the board, next to the battery, using tinned copper bus wire. The board has pairs of adjacent rows of connected holes, so I used two of these pairs (one row for each bus, each adjacent row for connections to the circuit).  The power rail is supplied from the voltage regulator circuit 5V output, and the ground from the 9V battery's negative lead. The positive lead from the battery goes to a 2-wire JST connector, which mates to another connector with leads going to a toggle switch. The other lead from the case (with the + from the battery) is the 9V input to the voltage regulator.
  5. Test the Voltage Regulator Circuit
    Since I have habit of messing up connections, and power is a key part of this, I wanted to be sure that I was getting 5V out of this part of the circuit before completing the soldering. When I got it right (after some stupid soldering tricks), I was ready to move on.
  6. Mount the components
    All the components had male headers attached, because I originally set set this up for a breadboard, so I soldered the headers to the printed side of the board. I also added an LED and resistor for visual representation of the sleep mode (the code for this was already included, so what the heck).
  7. Test the circuit
    Before fastening the circuit board to the enclosure, make sure everything works.  Here's where I ran into trouble.  I worked the continuity function of my multi-meter extensively. I thought I had everything in order, but it failed. I went back to a version of the sketch that had serial commands for testing in it, and saw that the SD board was not initializing.  I rechecked the connections, checked the SD card to see if it could be read, and then got drastic:  clipped the jumpers from the mini to the SD reader, and connected them via alligator leads to another reader.  Still not initializing, so I was pretty sure it was my connections.  One more continuity test revealed a problem with one of the jumpers. I re-soldered, put it back together, and it worked. Stupid soldering tricks, indeed!
    Working circuit, mounted. Clockwise from upper left: Adafruit Class D Mono Amp (wires to speaker), voltage regulator circuit, indicator LED and resistor, Pro Mini, Micro SD Card Reader. Yellow and green wires go to HC-SR04, red and black wires on right are power to HC-SR04 (red and black) and from 9V battery and switch (black and gray). 
  8. Put it in the box
    See photo at the top of this post.  Enclosing was a matter of adding screws in the prepared holes to secure the PCB, then passing the 4 wires to the HC-SR04 through one hole and the battery connection through another, position the speaker under the holes, and closing the box.
  9. Video
    Available on Youtube (my channel)