| This circuit board was developed for the BugBot project, however it's such a good design I think I'll use it for ZiBOT. | |
 Click on image for larger view. |
Bugbots Ultrasonic Board MkII. Features:
Additional requirements:
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| The redesigned MkII
board is stand alone, has it's own 5V supply regulated from a 9V
battery, generates all it's own timing signals. It also requires no
setup or adjustments and is about 50% smaller than the MkI. This design also uses a voltage doubler (ICL7760SCPA) to generate a +18V supply for the op-amps and ultrasonic outputs. This makes the design more stable, the high gain being achieved with out the need to tweak a potentiometer for max amplifier gain. The Schmitt trigger has been replaced with a comparator (LM393 dual comparator) this can be adjusted right down to 0V ref voltage. Whereas the Schmitt trigger has to be tweaked to give approx 0.5 to 1.0 volts whilst giving a stable o/p.The new circuit no longer uses a fixed reference voltage for the Schmitt trigger (comparator). It generates a decreasing exponential voltage that reduces the sensitivity of the circuit at the crucial early stages after the transmit cycle, when the o/p is still ringing and the receiver is still picking up the direct signal from the transmitter. This allows the circuit to detect an echo as close as the two sensors are apart. However after this initial stage the reference voltage for the comparator drops to near zero and becomes increasingly sensitive as the returning echoes become increasingly smaller. Thus increasing the range of the device.
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