Clock Circuits

A motor spins the "propeller", and a small microprocessor keeps track of time and changes the pattern on seven LEDs with exact timing to simulate a 7 by 30 array of LEDs. It is an illusion, but it works nicely.

When you think of clock synthesis, you typically think of simple digital division or a PLL. However, using a wire delay line and an unusual circuit known as a "tanktwanger," you can produce a clock generator with numerous advantages, including phase that is continuously variable.

This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily (see Notes).

Serial-data systems often generate an internal clock at twice the data rate for mid-bit sampling or for generating bi-phase codes. External equipment and some internal processes require a clock that runs at the data rate.

The purpose of this application note is to design a clock while multiplexing the features as much as possible, allowing the circuit to use the 18-pin PIC16C54. Other devices in the Microchip line expand on this part, making it a good starting point for learning the basics.

The simple, inexpensive circuit in Fig 1 provides backup power to a clock IC during outages. The circuit also determines whether the outage caused any loss in the time setting. C1provides the backup power, and the µC's ADC reads the time after the outage.

The oscillator circuit is one of the most overlooked areas of microprocessor circuit design. Components are usually selected based on the manufacturers? tables. If the circuit starts up and works, fine, no other thought need be given to it, right? Wrong. Many conditions can negatively affect the performance of your design.

This circuit demonstrates how to use bootstrapping to seriously boost the output power of the timer. The LC555 can only put out about 50mA as it is. This circuit can put out at least 200mA and goes to the rail as well.

About every year I design and build a new clock. This year’s project is a clock based on an Intel 8008 first generation 8 bit microprocessor. Because it is a fairly unique project I’m putting more effort into the documentation. I’m also totally opening the design, hardware and software, to anyone wanting to learn more about the 8008.

This circuit has worked for me in many applications. (it might be an idea to buffer the signal befor using it. (There are still 5 unused gates in the 'C14.. :-)