Due credit to James W.Elkins - KA8PH0, for the original design. His version differed slightly in that the LED's on his display board were spaced too far apart for my liking... Ugly! I redrew the pcb's to not only have the LED's closer, but to make things easier when soldering both boards together. That said, the rest is pretty much the same as the original.

Resistors R1, VR1 and R2 serve to scale the input voltage to a level that can be safely used by the A/D chip.
C2 (0.27uF), is a critical component. This is used for timing purposes for the A/D chip and should be of a high-quality polyester type. Capacitors C1, C3 and C4 smooth and decouple any noise present on the supply. Transistors Q1, Q2 and Q3 are used as digit driver buffers along with their current-limiting resistors, R5 through R7.
Four on-board test points (TP1 through TP4) have been included to be used during calibration.

DIL sockets, resistors, trimpots, capacitors, diodes, transistors, voltage regulator (on heatsink), two 2-way screw terminal connectors, and finaly, the four off-board connection solder pins (TP1 - TP4).

When you reach this stage, it's up to you to decide how you want to connect the two boards. Some homebrew'ers use ribbon cable. But, because I find this stuff difficult to work with, I opted have the boards placed back-to-back and interconnected with 11 resistor leads. From experience this is by far the easiest method. It's also a good idea to insulate these leads with sleeving. So why didn't I do that..? Because I didn't think of it until after they were soldered!

You'll notice that the interconnection pads between both boards will align hole-for-hole. e.g: pin 1 to pin 1... pin 2 to pin 2, etc. Looking at the picture you can see where I've used the eleven resistor leads used to make the interconnections. A 10mm spacer was used between the relevant holes on both boards to hold them parallel before the resistor leads were soldered proper. The two outer holes on the display board are used to support the unit to a fascia panel with two 10mm spacers.
If you decide to use this method make sure to solder the resistor leads in the main board first. You'll find it much easier when it comes to soldering the opposite ends on the display board due to its slight overhang.

When you reach this point you'll probably be itching to power-up to see the LED's a-glowing... but WAIT!! Spend some time checking both boards for any unwanted dry joints and/or solder bridges. We've all made these mistakes at some time, so take your time to check things through. (I use a small magnifying glass for such purposes).

• Adjust VR2 for a reading of 900 millivolts (0.9V).
• Disconnect your multi-meter when this has been set.
• Attach the test lead with clips to TP2 and TP3.
• Adjust VR4 for "90.0" on the DVM display. Disconnect the test lead when done.
• Solder a short insulated length of wire to TP1 and TP3.

Finaly, connect a known voltage source to the d.c input terminals and adjust VR1 to have the display read this known voltage. The on-board regulator will serve as a voltage source here. If you connect the test wire between the "+" side of C4 and the top end of R1, adjust VR1 to read "05.0" on the display.

And that's all there is to it.

The finished unit shown here has a polarised filter robbed from an old CB radio placed over the LED's. As luck would have it, it fits perfectly on the display. Unfortunately, the flash on the camera doesn't do this picture much justice - the reality is a much sharper display than shown here.

I've also tried green 7-segment LED's...

...and I still can't make up my mind which color I prefer.

And while we're on this subject, some of you ask where you can obtain components. Here in the UK I use various suppliers. You can find more details on the Links page under the heading, 'Suppliers'.
Maplin and RS (Radio Spares) are two major supplier here. Tandy is another good source, but sadly no longer trading in the UK. But since this hobby is about home-brew, you can find loads of cheap parts at local rallies, etc. Yet more sources of components are from old or broken equipment. Satellite receivers, radio's, TV's, Hi-fi's, etc... they all have something worth salvaging.
And since all my projects use ball-park components, you shouldn't have much problem finding 'em.