Circuits & Schematics - 5

A previous Design Idea “Gated 555 astable hits the ground running” ( Ref. 1 ) offered a fix for the problem of the excessively long first pulse that’s generated by traditional topology 555 astable circuits on start up when gated ...

While refurbishing an ageing audio mixer, I decided that the level meters needed special attention. Their rather horrible 100 µA edgewise movements had VU-type scales, the drive electronics being just a diode (germanium?) and a resistor. ...

The classic and versatile 555 finds its way into many low to moderate frequency oscillator applications. Some of these require the ability to selectively gate oscillation on and off on demand and the 555’s RESET pin can conveniently be used ...

Keeping op-amp outputs “live” at and below zero volts, generating symmetrical output signals, and processing bipolar analog inputs, are all examples of design situations where a few milliamps of negative voltage rail can be a necessity. ...

Second test circuit I looked at several types of AGC circuits (strictly, Automatic Level Control). JFETs are the usual starting-point but are inherently non-linear and need to be surrounded by lots of stuff to limit the signal voltage across them ...

A while ago, I needed (or wanted) a pocket-sized audio sine-wave generator: simple, stable, repeatable, single-gang control pot, 9 V battery-powered. A “squashed tri-wave” approach looked appropriate. While the principle is easy make a ...

The control circuit in Figure 1 senses a given load and automatically soft-starts the load by synchronously adjusting the power to that load. You can also manually adjust the power delivered to the load by controlling the phase angle of the line ...

Awhile back I published a simple design idea for a thermal airspeed sensor based on a self-heated Darlington transistor pair ( Ref. 1 ). See Figure 1. Figure 1. Older design idea with self-heated Darlington thermal airflow sensor. In the circuit, ...

To control their brightness, LEDs need a constant current; this can be done with a resistor placed in series with the LED string. Both the LED-string voltage and the supply voltage can vary, so a dedicated LED driver is a must to guarantee the ...

Intrinsically capacitive transducers and other high-impedance signal sources usually require ac coupling and a buffer amplifier to condition the signal for further processing. Buffers take many forms, but most of them compromise signal quality ...