improved vibrating battery

Posted on Feb 6, 2014

Many blind and deaf-blind people use portable electronic devices to assist their everyday lives but it is difficult for them to test the batteries used in that equipment. Talking voltmeters are available for the blind but there is no commercially available equivalent usable by deaf-blind persons. This device enables blind, deaf-blind and sighted p

improved vibrating battery
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eople to test batteries. It will test AAA, AA, C and D cells, as well as 9V "transistor" batteries. All rechargeable and non-rechargeable cell types are supported. The circuit needs no calibration. To use the tester, turn potentio-meter VR1 fully counter-clockwise and then connect the battery to be tested to the appropriate set of test terminals. If the battery has any usable charge, the pager motor in the tester will immediately vibrate. VR1 is then slowly rotated in a clockwise direction just far enough to stop the vibration. The position of VR1 then indicates the loaded voltage of the battery on a scale of 1-1. 5V (if the battery is connected to the 1. 5V test terminals) or 6-9V (if the battery is connected to the 9V test terminals). A regulated +5. 1V rail is generated from the battery under test with the aid of zener diode ZD1. For 9V tests, a 150O resistor limits the zener current, while diode D2 protects the circuit from reverse polarity battery connection. For 1. 5V tests, a blocking oscillator formed by Q1, Q2 and L1 steps up the battery voltage before it is applied to the regulator. This configuration works reliably with inputs down to below 0. 9V. The output of the oscillator is rectified by D1 and smoothed by the 33 µF capacitor. The circuit has to survive reverse connection of the battery under test. This creates a problem, because the LM393 cannot withstand a voltage more negative than -0. 3V at its inputs....

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