No volts

When Hans wired up the comparator circuit he could not get the output to go high. He swapped out the sensor with a simple voltage divider but still nothing. Thinking that he'd got a duff component he tried another, still the output stayed on 0v. The data sheet provided a clue, the output needed a pull up resistor, it could only act as a current sink.

Driving CMOS

The resistor was added and the voltage divider circuit behaved as expected, switching from low to high as the trim pot was adjusted.

 

Updated circuit

The full circuit was re-instated and that also tested successfully.

Comparator on boardboardPiezo Comparator Circuit 2

This circuit would ideally be tested with an oscilloscope so you could see the low voltage jagged signal from the piezo transducer and the clean output from the comparator. Not having a scope, Hans tested it with his trusty multimeter checking that there was a good swing on the output when he tapped on the transducer. Even on the input, the transducer seemed to be able to create voltages up to 3v which is quite bizarre thinking that it's just a sliced up piece of rock.

 

Boarding it up

Given that there were no special requirements for the board and the component count is low, stripboard was chosen for making up the circuit. Also the protoboard was already full and there was some stripboard in the back of the spares drawer. The board layout was sketched on lined paper and then the parts were test fitted on the board to ensure there was space for everything.

ComparatorStripboard.jpg

There was not much space in their extension so the new board was placed in the loft also meaning that the wiring to the transducer could be kept short.

RoofElectronics.jpg

Another cable was made up to connect this back to the main board and a hole drilled in the back of the roof space to fit the connector through. A wooden support was made to hold the board to the roof and the transducer was connected using double sided tape.

 

Next: Enchanted Objects Design Challenge - The Crystal Cave