CGS quad logic gate (previous version)

CGS39 the CGS quad logic gate is a very simple module that can be built in one of five flavors : XOR, OR, AND, NOR and NAND. It is a simple way to gain additional control of gate and trigger pulses within a system. It can also be used for some simple signal multiplying. The XOR is well known as a square wave "ring modulator", though interesting effects can also be generated using the other configurations. Each gate has an in-built LED to indicate the status of the output of that gate.

With some chip types, it is also possible to have some of the gates presented on the panel as basic inverters. For XOR and NOR gates, tie the disused input of that gate to 0V. For NAND gates, tie the disused input of that gate to +15V. It is not possible to create inverters with AND and OR gates.

While untested, the module should work on 12 volts.

A little on how it works
Connection/pin identification table for the above diagram. Note that there are two LM324 chips involved, one for In 1 and 2, the other for In 3 and 4: Each input is configured to detect a voltage over approx. 2 volts. When this voltage is reached, a logic HIGH is presented to the corresponding gate input. The output will react to what is present at the inputs, and the result, depending on the gate chip used, is buffered by the emitter follower, and used to drive the LED and output jack.

Truth tables for the different logic gates that can be used in this circuit:

Construction
Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC socket if used, then moving onto the taller components.

Take particular care with the orientation of the polarized components such as electrolytics, diodes, transistors and ICs.

When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

In this case I recommend using a socket for the CMOS chip, as this will allow different chips to be substituted for the purpose of experimentation.

Valid choices are:
 * 4030 or 4070: XOR
 * 4001: NOR
 * 4011 or 4093: NAND
 * 4071: OR
 * 4081: AND

There are four LED return pads, marked LR1-4. The order in which these are used is not critical. Each pair of inputs to a gate share the same designator. The order in which each pair is wired to the panel sockets is not critical.

Parts list
This is a guide only. Parts needed will vary with individual constructor's needs.

CC-BY-NC
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.