Bluetooth Low Energy Remote Control

Bluetooth is a protocol where a Master communicates with one or more Slaves; the Slaves cannot talk to each other. The Master is often a smartphone or computer, but this isn’t always desirable. A Bluetooth Master module will work very well instead.

The basic circuit of the remote control is fairly simple (see Figure 1). In fact, because the BL620 can do everything itself, there’s no need for much extra besides. Two push-buttons and a two project color LED are enough; a reset button, programming connector, and switch for selecting the operation mode (debugging or run) complete the picture. The complications arise when we add the power supply.

fig 1 5 Bluetooth Low Energy Remote Control

Remote control implies battery. Remote controls are usually wireless and hence battery powered. Ours is the same, we’ll even be using a 12 V battery. So why this voltage, when the BLE module operates at 3 volts? It’s the result
of a compromise. The problem was to find a small standard case suitable for a remote control with a battery holder, two push-buttons, and LED, and of course with room for the BL620 (which measures 19 × 12.5 mm). The only case that met our criteria was intended for 12-V batteries (in fact, it is a case for a garage door-style remote control) – that’s why! We’re going to drop the voltage using a little bit of electronics, and for this task we’ve chosen the LTC3632 from Linear Technology (now Analog Devices).

For the longest battery life, the circuit’s consumption must remain as low as possible. There’s no problem in terms of the BL620, it draws only 0.5 μA in sleep mode, but the converter/dropper also has to be fed. Now believe it or not, it’s quite greedy: it draws 12 μA! This might not seem like very much to you, but in reality it’s much too much, as the 12-V batteries (in 23A format) usually have a capacity of only 55 mAh. So it’s out of the question to leave it powered continuously, which is why we’ve added an electronic on/off switch, with the help of a few transistors and diodes. Figure 2 shows the final circuit.

fig 1 6 Bluetooth Low Energy Remote Control

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13. February 2019 by sam
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