A To D Converter

Getting retro hardware up and running again is sometimes a feat, and the amount of effort needed tends to go up exponentially with increased hardware age. Getting an IDE hard drive running again is one thing, but things like peripherals on truly “retro” computers like Commodores and Amigas is another beast altogether if you even have a 30-year-old mouse still lying around. That’s why adapters like Project mouSTer are here to help you connect modern USB hardware to truly ancient computers.

This piece of equipment was built for the Atari ST (hence the name), a ~~8-bit~~ computer from the mid-80s. It mates a DB9 plug with USB via a small microcontroller which does the translating. The firmware can be flashed over the USB connection so there’s planned support for other machines of this vintage. The chip supports all the features the original mouse did, too, including PS4 pad support and support for joysticks, and comes in an impressively tiny package once assembled which blends in seamlessly.

The project is a great step to getting retro computers working again, even if you can’t find exact OEM replacements anymore. That’s a common problem, and we’ve seen this solved in other ways for other old Ataris. It’s not uncommon to put modern power supplies in retro computers, either, as long as they power up and work after everything’s wired together.

Riffling through my box of old projects, I came upon a project that I had built in the 80’s — an Automotive Multimeter which was published in the Dutch/British Elektor magazine. It could measure low voltage DC, high current DC, resistance, dwell angle, and engine RPM and ran off a single 9V battery. Besides a 555 IC for the dwell and RPM measurement and a couple of CMOS gate chips, the rest of the board is populated by a smattering of passives and a big, 40 pin DIP IC under the 3½ digit LCD display. I dug some more in my box, and came up with another Elektor project from back then — a True RMS digital Wattmeter with a 3½ digit LCD display that could measure up to 2kW. It had the same chip too. Some more digging, and I found a digital panel meter. This had a 7 segment LED display, but the chip was again from the same family.

Look under the hood of any device with a 3½ or 4½ digit, 7 segment, LCD or LED from the ’80’s or ’90’s and you will likely spot this 40-pin DIP with the Intersil logo (although it was later also manufactured by many other fabs; Harris and Maxim among others). The chip doing all the heavy-lifting was likely to be the ICL7106 or ICL7107. These devices were described as high performance, low power, 3½ digit A/D converters containing seven segment decoders, display drivers, voltage reference and clock. In short, everything you needed to take a DC analog signal and display it. Over time, a whole series of devices were spawned:

7106 – 3½ digit, 7 segment LCD
7107 – 3½ digit, 7 segment LED
7116 – 3½ digit, 7 segment LCD, with display HOLD (freeze)
7117 – 3½ digit, 7 segment LED, with display HOLD (freeze)
7126 – improved 7106
7136 – improved 7126
7135 – 4½ digit, 7 segment LCD

There were many similar devices available, but the ICL71xx series was by far one of the most popular, due to its easy of use, low parts count and single chip implementation. Here are several parts (linking to PDF datasheets) to illustrate my point: the TC14433/A needed several peripheral devices, ES5107 (a clone of a clone — read below), CA3162 (which has BCD output, and needs the CA3161 or similar to interface to a display), or the AD2020 (which too needed a lot of support circuitry).

The ICL71xx was the go-to device for a reason. Let’s take a look at the engineering and business behind this fascinating chip.

Continue reading “Get To Know 3½ Digit ADCs With The ICL71xx” →