Lab 0: Wire Wrapping Project: Counter Board

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In this experiment, you will build a simple counter circuit that can be plugged into your breadboard. It will provide a set of TTL output signals at various frequencies for use as clock inputs or other applications. The design of this board is simple and compact. It will be built on a piece of perf board (a modular circuit board with pre-drilled holes) with a row of pins for easy connection to jumper wires or breadboards. Connections will be made using the wire-wrapping technique.

This circuit is centered around the 74HC4040 ripple counter whose outputs divide the input signal by two for each successive output. There are 12 outputs, so the slowest output is the input frequency divided by $2^{12}$ . By using two ripple counters, we will build it such that you will be able to select from several different ranges of frequencies. The input clock source comes from a 1 MHz oscillator fed through a Schmitt trigger for a clean TTL signal.

1. Layout: The perf board will provide the structure to construct the circuit. Each of the components will be tacked onto the board then connections will be made with wrapped wires on the back side. We will use pin headers both to provide connection points for power, ground, and outputs, and also to make a jumper bank for selecting the speed of the outputs.

2. Design: This design uses an oscillator crystal to generate a 1MHz square wave that is passed through a Schmitt trigger to ensure the signal has square edges. The output of the Schmitt trigger is sent to the 4x2 pin header and to the clock input of one of the ripple counters. The four connections to one side of the 4x2 pin header are the output of the Schmitt trigger and the 4th, 8th, and 12th outputs of the first ripple counter. These are used to feed varying clock speeds into the second ripple counter, thus controlling the frequency options for final output of the circuit. On the other side of the 4x2 header, all four pins connect to the input of the second ripple counter, such that when you move the jumper block from one pin pair to the next, you are adjusting the input to the second ripple counter. The first pair of pins makes a direct connection from the oscillator/Schmitt trigger making a 1 MHz input to the second ripple counter. The second pair uses the 4th output of the first counter, scaling the 1MHz oscillator to an intermediate frequency of 62.5 KHz, the third pair uses the 8th output scaling the intermediate signal to 3.9 KHz, and the fourth pair uses the 12th output scaling the intermediate signal to 244 Hz (the fourth pair). Each of these can be used to feed the input of the second 74HC4040 counter thus scaling the outputs by $2^4$ for each subsequent jumper position.