SN74HC595 Test Module

This is a test module with a specific function, to test SN74HC595 shift registers. I am making a Arduino Binary Clock Shield and I wanted a way to verify the HC595s before using them.

I found a circuit on YouTube for an LED sequencer and decided to make that circuit into a Test Module to verify 74HC595 ICs are working properly, and this is the module I came up with. This module is powered by 5 volts either from a plug or from wires with Dupont female pins.

The operation is quite simple, if you can see the left to right sequence of LEDs changing, your HC595 under test is working, as simple as that.

This is a basic circuit that you can have assembled in an hour. Basic soldering skills are needed as well as reading schematics.

Component functions will be described during the assembly.

Parts:

Note: resistors are all 1/4 watt, and you can use 5% or 1% tolerance depending on what you have on hand, nothing critical with the values.

74HC595 Test Module PCB, available here on PCBWay (coming soon!). The Gerber zip and schematic are available on my proton drive here.

16 pin ZIF socket, x1

8 pin DIP socket, x1

330 resistor, x1

1K resistor, x1

20K resistor, x2

50K 3296W trim pot, x1

100nF 50v monolithic disc capacitor, x2

10uF 25v electrolytic capacitor, x1

10uF 35v electrolytic capacitor, x1

BC547 transistor, x1

LEDs 5mm, x8, any color (I used orange as I had a lot of them on hand)

LM555 Timer IC, x1

74HC595 shift register, x1 (known good, for testing circuit)

male header pins, 2.54 pitch 2P (or as I did you can use 1 red pin and 1 black pin)

SPDT mini slide switch, 3 pins, x1

PC mount DC barrel jack, x1 (center pin is + so your power supply should be + center pin as well)

standoffs, the mounting holes are 3.5mm, (I used nylon M3x4 screws and M3x6 standoffs).

Tools:

schematic, available on my proton drive here.

soldering iron and solder.

liquid flux and braid, in case mistakes are made.

breadboard, or Pin Header Soldering Tool

flush cutters

tape, for holding parts while soldering.

5 volt power supply, so you can test the module after it is completed.

When assembling electronics projects I normally start at the lowest and work my way up to the tallest parts, however, when it comes to male header pins, much easier if you install those first. Use a breadboard or a pin header soldering tool, insert the pins upside down and place the PCB upside down onto the pins and solder them in place.

Next comes the lowest profile parts; resistors, monolithic disc capacitors, and the DIP 8 socket.

H1, if one is use a power supply module or a supply with two wires with female Dupont pins, the + and - 5 volts is plugged in on these, I chose to use a red pin for + for positive and a black pin for ground, feel free to use just a 2P header if you like as the pins are clearly marked.

R2, is for current limiting on R1.

R3, is for current limiting on the serial input of the 74HC595.

R4, is for current limiting on the base of Q1.

R5, is for current limiting on LEDs D1 through D8.

C1, C3, are decoupling capacitors for U2 and the 74HC595 under test.

U2, is the 555 Timer, and provides the clock from pin 3 to the 74HC595 under test on on pin 11.

Now you can add the taller profile parts, the order in which I installed these in this order; SW1, Q1, R1, C2, C4, 16 pin ZIF socket, and finished up with D1 through D8.

SW1, on provides 5 volts to the circuit, and off simply turns off the 5 volts.

Q1, is the gate for the serial input, a pulse comes from pin 7 (output 7) of the shift register and is gated through the base of Q1 and the collector of Q1, which sends a serial input to pin 14 of the shift register. (I really hope I got that description correct, but you should get the gist of it!)

R1, is a trim pot, part of the RC circuit, in conjunction with C2, and is used to increase or decrease the clock going to the shift register.

C2, part of the RC circuit, in conjunction with the adjustment of R1.

C4, is a filter cap to smooth the power coming in either through the J1 or the header pins.

16 pin ZIF socket, this will hold your 74HC595 under test. Keep in mind, the handle of the ZIF goes towards the edge of the PCB, as shown on the silkscreen. When inserting a HC595, the notch goes towards the handle end, or towards the edge of the board, pin 1 is also marked on the silkscreen for the location of pin 1 on the IC.

D1-D8, are LEDs to show the output of the shift register.

Once you have all the parts soldered in, now you can attach the standoffs, then insert a 555 Timer into the 8 pin socket, making sure the notch on the IC is placed where the notch on the socket is. Your Test Module is now complete, ready for testing.

Place the ON/OFF switch to OFF.

Plug in a 5 volt power source, either with a barrel jack or wires with female Dupont connectors.

Insert a known good 74HC595 IC into the ZIF socket and lock the handle down, the notch on the IC goes towards the handle end of the socket, and pin 1 is also marked on the PCB where pin 1 of the IC goes.

Slide the ON/OFF switch to ON.

The LEDs will not be lit, then the far left LED will light, and will shift right and the next left LED will light, and so on until all the LEDs are lit, the starting from the left, an LED will go out, then that shifts to the right with the next LED going out, and continues until all the LEDs are out, then process starts again with the leftmost LED lighting, shifting to the right with the next left coming on, as shown in the video.

Is this a useful tool for everyone? Certainly not, unless you are using a lot of SN74HC595 shift registers. Do I find it useful, yes.

Arduino users, such as myself, may find this useful when putting together a project and nothing seems to be working correctly, it could very well be a bad shift register(s). If you just need to test 1 or 2 for small project, you can assemble this on a breadboard if you like.