CGS quad logic gate

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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

Quad logic gate schematic. Click through for larger.

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:

4001
NOR
IN a IN b OUT
0 0 1
0 1 0
1 0 0
1 1 0
4011, 4093
NAND
IN a IN b OUT
0 0 1
0 1 1
1 0 1
1 1 0
4071
OR
IN a IN b OUT
0 0 0
0 1 1
1 0 1
1 1 1
4081
AND
IN a IN b OUT
0 0 0
0 1 0
1 0 0
1 1 1
4030, 4070
XOR
IN a IN b OUT
0 0 0
0 1 1
1 0 1
1 1 0

Construction

The component overlay. Connections can be determined from the circuit diagram.
Click through for 300DPI printable overlay.

Due to a manufacturing error, the overlay on one version of these PCBs has become cluttered. Print out the above file to assist with assembly.

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 resistors, marked RL. The value of these is determined by the type of LED you have chosen. Try out your LED with various resistors before assembling the board. If you are using common LEDs, 1k to 2k2 would be appropriate. If you are using any of the super-bright modern LEDs for their unique colors, the resistors can be much higher, 10k to 33k for example, so that the LEDs don't dazzle you.

There are five 100n decoupling capacitors. These can be 1206 SMT or regular capacitors. The one on the logic chip must be mounted on the rear of the PCB regardless of the chosen type.

Parts list

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

Part Quantity
Capacitors
100n (can be SMT1206) 5
10uF 25V 2
Resistors
1k 4
1k8 4
RL See text 4
10k 8
15k 2
100k 26
Semi's
BC547 or sim. 4
CMOS Logic chip 1
TL074 2
Misc
Ferrite bead (or 10R resistor) 2
0.156 4 pin connector 1
CGS39V2 PCB 1

Notes

  • A 10 to 22 ohm resistor can be used instead of the Ferrite bead. If you don't care about power-rail noise, just use a link instead.
  • PCB 6" x 1" with 3mm mounting holes 0.15" in from the edges.

CC-BY-NC

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

See also

References

External links

Suppliers