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DIY Roomba Virtual Wall, Part 2

Following on the success of the test circuit, I added a status LED and a pushbutton to the breadboard. 

A summary of the connections:

  • IR LED connected to pin 3 (PB4) of the ATtiny85 (100ohm current- limiting resistor). Pin 3 is where the tiny_IRremote library sends its output to by default.
  • Normal LED connected to pin 2 (PB3, 220ohm current-limiting resistor). We will use this LED as a status indicator to 1) signal power-on 2) signal battery low
  • Pushbutton connected to pin 6 (PB1, 10Kohm pull-up resistor). We will use this as a soft switch to turn the virtual wall on/off.

The Arduino source code is available here.

Note: I configured ATtiny85 to run at 1MHz for additional power saving. Correspondingly, in tiny_IRremoteInt.h, I had to change #define SYSCLOCK from 8000000 to 1000000.

Some highlights of the code:

  • Pin change interrupt is used to monitor when the pushbutton is pressed to turn on the unit.
  • In normal operation, status LED flashes every second.
  • Watchdog timer interrupt is triggered every 64s to measure the battery level. If battery level drops to below 2.8V, status LED flashes 0.1s every 4 seconds to signal that battery needs to be changed.
  • The circuit automatically turns off after 80 minutes.

I powered the circuit using 3xAA NiMH rechargeable batteries. Since the operating voltage of the ATtiny85 is 2.7V - 5.5V, 2xAA alkaline batteries will also work. But with 3xAA, both rechargeables and alkalines can be used, so I went with that.

Using the current meter to measure,  when the circuit is off, the current consumption is around 0.2mA. When the circuit is on and emitting signal, the current consumption is around 5.5mA.

At 2000mAH per AA NiMH battery, this works out to 363 hours of continous operation. If the unit is run for 2 x 80 minutes every day, the battery would still last for at least 3 months, which is good enough for me. Plus I much prefer to work with AA rechargeables than C-size batteries which the original virtual wall requires.

I soldered the components down onto a prototype board, and here's what I came up with:

The prototype board is 5cm x 7cm cut in half, so the dimension is 5cm x 3.5cm.

The IR LED is the one jutting out horizontally in front. The white 2-pin JST female connector is for interfacing with the battery holder.

A 0.1uF ceramic capacitor is added between the VCC and GND pins of the ATtiny85 for decoupling purpose.

In the next step, I will 3D print a suitable enclosure for the virtual wall.

Part 1 - Part 3 - Part 4

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