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LED Wink Testers For 1.5 Volt Cells
They wink if the battery is not dead yet.
Find updates at www.projects.cappels.org
This page contains a collection of circuits that wink when the power switch is thrown to indicated whether the 1.5 volt (and other voltages near 1.5 volts) cell still has a significant charge left. Choose the best one for your application.
Lowest Energy Use Red or Green Wink Tester Using DPDT Switch
This circuit only uses the energy necessary to charge the capacitor each time the switch is moved to the "OFF" position, but that comes at the cost of the need for a DPDT switch. After the 330 uf capacitor is charged and when the switch is moved to the "ON" position, the capacitor is placed in series with the 1.5 volt cell and the LED, which makes 3 volts available to drive the LED through its current limiting resistor.
Do not use the circuit of figure 1 with a battery voltage of greater than 1.5 volts( the forward drop of the LED), otherwise, C1 would be slightly reverse biased after discharging.
Low Power Use Red or Green Wink Tester Using SPST Switch
The circuit of Figure 2 is similar to that of circuit 1, except that one pair of switch contacts is replaced with the upper 10k resistor. The fact that the lower 10k resistor is not swiched out of the circuit means that when operating from a fully charged 1.5 volt cell, 225 microwatts will be dissipated during the time the switch is in the ON position.
Do not use the circuit of figure 2 with a battery voltage of greater than1.5 volts (the forward drop of the LED), otherwise, C1 would be slightly reverse biased after discharging.
Low Power Use Red Or Green Wink Tester With Fast Recovery Using SPST Switch
The circuit of Figure 3 is similar to that of figure 2, except that the upper 10k resistor is replaced with a small diode to assist in quickly charging the LED after the power switch is moved to the "OFF" position, thus allowing the full "wink" even if power was removed for only a second or two.
Do not use the circuit of figure 3 with a battery voltage of greater than1.5 volts (the forward drop of the LED), otherwise, C1 would be slightly reverse biased after discharging.
Low Power Use White Or Blue Wink Tester Using SPST Switch
The circuit of Figure 4 is based on a completely different concept. Instead of charing a capacitor that is then placed in series with the cell, a step-up converter is used to boost the 1.5 volts to 3 volts or more to power a blue or while LED, befor a 100 uf capcitor charges, allowig the lower transistor to shut off the oscillator. This is a modification of the 1.5 volt white LED driver, http://cappels.org/dproj/ledpage/leddrv.htm. Details of designing the step-up supply can be found at the URL provided.
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First posted in February, 2013. Typo corrected March, 2013.You can send email to me at projects(at)cappels.org. Replace "(at)" with "@" before mailing.
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