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Step 3Trigger Voltages
The table below shows the approximate turn-on voltages for various combinations of diodes and LEDs that have been tried in the the trigger string of various Easter engines. All of these trigger combinations can be fit onto the stripboard layout of the previous step, but the 4-diode and 1 LED combination would have to have a diode-to-diode joint soldered above the board.
The LEDs used in making the table measurements were older low intensity reds. Most other newer red LEDs that have been tried work about the same, with maybe a variation of only about plus or minus 0.1V in their trigger level. Color has an influence: a green LED gave a trigger level of about 0.2V higher than a comparable red. A white LED with no diodes in series gave a turn-on point of 2.8V. Flashing LEDs are not appropriate for this engine circuit.
A useful feature of the Easter engine is that the turning-off voltage can be raised without affecting the turning-on level by inserting one or more diodes in series with the base of Q2. With a single 1N914 diode connected from the junction of R4 and R5 to the base of Q2, the circuit turns off when the voltage drops to around 1.9 or 2.0V. With two diodes, the turn-off voltage measured approximately 2.5V; with three diodes, it turned off at about 3.1V. On the stripboard layout, the diode or diode string can be located in place of the jumper shown above the resistor R5; the second illustration below shows one diode D0 thus installed. Note that the cathode end must go to the base of Q2.
Thus it is possible to effectively use the Easter engine with motors that do not run well near the basic turn-off of about 1.3 or 1.4V. The solar engine in the toy SUV in the photo below was made to turn on at 3.2V and turn off at 2.0V because in that voltage range the motor has good power.
The LEDs used in making the table measurements were older low intensity reds. Most other newer red LEDs that have been tried work about the same, with maybe a variation of only about plus or minus 0.1V in their trigger level. Color has an influence: a green LED gave a trigger level of about 0.2V higher than a comparable red. A white LED with no diodes in series gave a turn-on point of 2.8V. Flashing LEDs are not appropriate for this engine circuit.
A useful feature of the Easter engine is that the turning-off voltage can be raised without affecting the turning-on level by inserting one or more diodes in series with the base of Q2. With a single 1N914 diode connected from the junction of R4 and R5 to the base of Q2, the circuit turns off when the voltage drops to around 1.9 or 2.0V. With two diodes, the turn-off voltage measured approximately 2.5V; with three diodes, it turned off at about 3.1V. On the stripboard layout, the diode or diode string can be located in place of the jumper shown above the resistor R5; the second illustration below shows one diode D0 thus installed. Note that the cathode end must go to the base of Q2.
Thus it is possible to effectively use the Easter engine with motors that do not run well near the basic turn-off of about 1.3 or 1.4V. The solar engine in the toy SUV in the photo below was made to turn on at 3.2V and turn off at 2.0V because in that voltage range the motor has good power.
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