A start-up circuit having a micro crush capacitor that is operatable with a small pressure. The crush capacitor may be connected to a silicon controlled rectifier or similar device. Applying the pressure to the crush capacitor may turn on the SCR which may in turn activate a sensor. The circuit may be fabricated on a flexible substrate which together may be regarded as a flexible circuit. The flexible circuit may be held down on a back plate with a form plate clamping the circuit at its perimeter edge. The flexible circuit may be held firm with the plates for component insertion and/or circuit testing.