CD4033 & 7-segment LED Tester

I am currently working on a project that has a lot of CD4033 ICs and 7-segment LEDs, so I fabricated a tool to test the ICs and the LEDs to show functionality.

The clock input is manual with a simple pushbutton, no external clock circuit is needed. This tool is configured to provide ripple blanking, meaning if there is no digit from the counter, it will blank the LED instead of showing zero or a leading zero when testing two ICs. Lamp Test is also a feature of the tool to test the LED displays. And there is a Clock Inhibit switch to simple turn on or off the clock input. The Reset button resets the IC to indicate blank displays.

This tool can be powered with a standard wall adapter of 5, 9, or 12 volts. When 9 or 12 volts in selected, a manual selection, a 5 volt regulator provides the clean 5 volts.

Circuit description will be stated during the installation steps.

For this Instructable, you should have knowledge of reading schematics and basic soldering.

Parts List: resistors are 1/4 watt 5%.

PCB, x1 (you can order here on PCBWay (affiliated), and here is the Gerber file on my proton drive.)

CD4033BE decade counter with ripple blanking, x2 (for testing)

16 pin ZIF socket, x2

5161AS common cathode 1 digit .56 display 7-segment display, x2 (for testing)

LM7805 5 volt regulator plus heatsink, screw, isolation washer, silicone pad, x1

10K resistor, x4

330 resistor, x1

1N5819 Schottky diode, x1

100nF 50 volt monolithic disc capacitor, x4

10uF 25 volt electrolytic capacitor, x2

green 5mm LED, x1

2 pin tactile switch, x3

mini slide switch SPDT 3 pin, x3

PCB mounted DC jack 5.5 x 2.1

female machined header pins single row 2.54 spacing, 4 pieces of 1x5.

standoffs and screws, x4 each (I use 3mm screws and 6mm long standoffs)

Tools:

Schematic

Soldering iron and solder

flush cutters

Solder wick and liquid flux (if mistakes are made)

electrical tape

Go ahead and install standoffs in each corner, this keeps the back of the board off your workbench. You will need the schematic for the assembly since I do not use values on my schematics, only reference numbers.

Normal practice is to install from lowest profile components to the tallest. So first form the leads for the resistors and diode.

Use tape to hold the component in place, then turn over and solder the leads. Remove the tape, check the solder on the top of the board, component level, then trim the leads with the flush cutters. Keep in mind the marking for the diode for the correct orientation. Solder in the small capacitors.

Functions:

D16 is a Schottky diode and is used to prevent voltage flowing back to the voltage regulator when using 5 volt input power.

R1, R2, R3, and R4 are pull down resistors and provide a ground on the CLK, LAMP, RESET, and CLKINH pins of the ICs when the when the buttons are not pressed and the switch is in the off position.

C2 and C3 are filtering on the voltage regulator.

C5 and C6 are decoupling caps for the ICs.

Next parts to go in are the tactile buttons and switches, and are very straightforward in installing those.

For the female header pins, these are going to be our sockets for the 7-segment LED displays. Snap the header pins into the 4 sections of 5 pins each. Take a 7-segment LED and insert the pins into the header, do this for both sets of leads on the LED. Now take the 7-segment display and insert into the board at the holes indicated for the display, tape the display in place, turn over, and solder one pin and the ends of each header row.

Turn the PCB over, remove the tape, LED stays in the header pins for this, and check that the headers are sitting flat on the board, if not, hold the board on its edge so you can see the soldered pins, and while pressing in the LED, place your solder iron on a pin that is too high, when it melts, you may hear a click when the header is flush. Do this the other row as needed as well. When you are satisfied that the headers are flat on the board, now you solder the pins in between the soldered pins.

Repeat this with the second LED display.

Functions:

SW1 is as stated, simply turns the circuit On or Off. When inserting or removing ICs or LED displays, turn the power off.

SW2 is the voltage selector, to the left is when using a 5 volt power supply and prevents the regulator from being used, to the right is for when using 9 or 12 volt power supply and turns on the 5 volt regulator.

SW3 is CLK, or Clock, and is a manual clock input to pin 1 of U1. Each press of this button increases the count on the LED display.

SW4 is LAMP, or Lamp Test, pressing this applies 5 volts to pin 14 of U1 and U2, and lights all the segments on each LED display, which will show an 8.

SW5 is RESET, pressing this applies 5 volts to pin 15 of U1 and U2, resetting the count to a blank display, with nothing lit.

SW6 is CLKINH, or Clock Inhibit, setting this to one applies 5 volts to pin 2 of U1, stopping the clock input.

LED1 and LED2, the female machined header pins are the sockets for the 2 displays, 1s is on the right, 10s is on the left. If only testing 1 CD4033 and one LED display, use the LED on the right and U1.

Next taller components to install are the DC jack, filter capacitors, and the voltage regulator. I was still waiting on the ZIFs to arrive to I skipped those for now.

The DC jack is straightforward to install. For the electrolytic capacitors, ensure you install with the correct polarity. The voltage regulator is straightforward, pin 1 is marked with the dot. You can easily let the heat sink set right on the board since you are only powering 2 ICs and 2 LED displays.

Functions:

J1, the DC jack, allows 5, 9, or 12 volts to be plugged into the tool, but keep in mind the switch setting of SW2, set that to the voltage of your power supply.

C1 and C4 are filter capacitors for the voltage regulator, one is on the input side and the other on the output side of the regulator.

U3 is the 5 volt regulator, yes, over kill with the heatsink but I like to add heatsinks to voltage regulators.

ZIFs are Zero Force Insertion sockets, which means with the lever upright, you place a CD4033 IC in a socket, then push the lever down to clamp onto the legs of the IC.

Place a ZIF for U1, tape in place, push the lever down, turn over and solder just one pin in opposite corners. Remove the tape and check that the socket is flat to the board, if it is, turn the board over and solder the other opposite corners to hold the socket firmly in place now, then solder the rest of the pins.

If the socket is not flat on the board, hold the board, edgewise down on the workbench so you can see the pins, hold the socket firmly, pressing down, and heat the pin when the socket is not flat, when it melts, you may hear a click when it seats firmly. Repeat for the other end if needed, then solder the other opposite corners to hold the socket firmly, then solder the remaining pins.

Repeat the second ZIF.

Soldering is now complete.

Insert two known good CD4033 ICs into the ZIFs and lock them in place. Insert two known good 7-segment displays into the headers for LED1 and LED2.

First, determine what power supply you are going to use, and set SW2 to the correct position, left for 5 volts, and right for 9 or 12 volts.

Photo 1. Plug in power supply and insert the plug into the J1. Slide the one off switch to On, D1 will light green.

The displays may show blank on both, but if there is numbers or random segments lit, press and release the RESET button to clear out the count and set both displays to blank. This is the ripple blanking working, since there is no number generated, no segments are lit. This tests the RESET function of the ICs as well as Ripple Blanking is working.

Photo 2. Press and release CLK button and the 1s digit should now show a 1. The 10s digit should still be blank since since the preceding zero is not to be displayed unless it is part of a number, like 10.

Photo 3. Press and release CLK button and the 1s digit should now show a 2.

Photo 4. Press and release CLK button until you have 10 showing, since the zero is part of a number, it will show. This tests that the clock function is working, and when using 2 ICs, it tests that the Clock Output function (pin 5 on U1) is working.

Photo 5. Press and release LAMP button, the LED displays should show all 8s which lights every segment in the display. This tests that all segments in each display is working and that the ICs are all working.

Now you can use the tool for testing CD4033 ICs and 7-segment displays.

I did notice sometimes the tool will advance the numbers too quickly, I think I just need to rework the debounce for the CLK switch (I may need to add a capacitor across the switch leads.

Also noticed sometimes the digits will glow very faintly after a reset or the leading zero will appear very faintly, simply holding the tool instead of resting on the bench cleared that up.

Other than those issues, I will say the tool works as designed. I hope you find this tool useful.