Nuts & Volts - September 2004

Just For Starters

and isolate analog signals better than a sequencer. The sequencer in Figure 5 is a 4017 decade counter and it produces a high output (equal to the power supply) at only one of its 10 outputs. The other nine outputs are low and all of the outputs are connected to potentiometers.

When a pulse is fed to pin 14, the counter advances to the next stage. Since only one diode at a time is high, it passes whatever voltage is set by its potentiometer to the output bus. This voltage reverse biases all other diodes, so they become highly resistive and isolate the nine low state outputs.

No interaction between stages will occur because only the voltage at the active stage will be passed to the bus. The result is a manually adjustable staircase wave shape. This circuit is ideally suited to operate voltage controlled oscillators and other electronic music circuits.

best in this circuit, but, if they are too bright, increase the value of resistor R1.

Because audio levels from music can be transient, signals may occur too quickly to be observed.

Capacitor C1 will help hold the signal long enough for it to be seen. If the capacitor does not hold the signal long enough, try a

larger value.

Conclusion

Diodes can help you achieve your circuit goals, whether you want to trigger an alarm, regulate a power supply, or light up a project with LEDs. The diode will point you in the right direction. NV

Integrated Circuits

Diode elements are etched into ICs to direct signals, prevent false triggering, and stabilize — as well as protect — the circuit. Tunnel diode doping techniques are being researched to increase the efficiency of the new breed of integrated circuits.

Bar Graph Sound Level Indicator

Figure 6 shows how to use diodes in series to set a “trip point.” Twenty-two diodes and six LEDs — along with three resistors and a capacitor — comprise this simple sound level indicator. The input accepts a high level audio signal through D1. As a low level signal rises in amplitude, it meets the biasing threshold of diode D2 and LED D23 lights. When the signal increases beyond the biasing requirement of D3 and D4, LED D24 will light. This process continues down the line to LED D28, as long as the signal level increases.