Battery Tester For Deaf and Blind Persons

Posted on Feb 6, 2014

Many blind and deaf-blind persons use portable electronic devices to assist their everyday lives but it is difficult for them to test the batteries used in this equipment. Talking voltmeters are available but there is no equivalent usable by deaf-blind persons. This battery tester uses vibration and a user-settable control to enable blind and deaf

Battery Tester For Deaf and Blind Persons
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-blind persons to test both ordinary and rechargeable AAA, AA, C, and D cells and 9V batteries. For ease of use and maintenance the device is powered by the battery under test. The design is dominated by the fact that the pager motor will operate down to only 0. 7V. With a 0. 3V drop from the switching transistor, a weak cell, at 1. 0V, will only just operate the motor. This means that the 1. 5V cell sensing circuitry cannot be isolated from the 9V test terminals using steering diodes - they would introduce too great a voltage drop. The solution was to duplicate the level sensing circuitry for each set of test terminals. On the 1. 5V side of the circuit, a resistance network consisting of two 10kO multi-turn trimpots (VR2 & VR3) and user control VR1a produces an adjustable proportion of the voltage of the cell under test. VR1a selects a division ratio between the low and high limits set by the trimpots. The resistance of VR1a is 10 times larger than the resistance of these trimpots to minimise the interaction between their settings. The voltage from the resistance network is applied to a combined threshold detector and current amplifier formed by Q1 to Q4 and associated components. When the threshold (about 0. 6V) is exceeded the pager motor is energised, causing the battery tester to vibrate. In use, VR1 is first set to its fully counter-clockwise position, then a cell is connected. If the cell`s voltage exceeds the 1V low...

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