Berkel 176SG digital scale (1980)

Cycling home on a rainy day, I saw this large scale standing on the sidewalk near a garbage container in the neighbourhood. I braked and picked it up, further walking home balancing this heavy object on my bicycle. I recognised the supports on the weighing platform from the scales in greengrocers' shops, they are intended to hold a metal bowl to weigh vegetables. I remember I saw a similar type of scale in a butcher's shop many years ago, with a flat, smooth stainless steel weighing platform.

Berkel was a Dutch manufacturer of meat slicing machines and weighing equipment for food shops. They have been taken over by Avery in 1993, but it seems they are still selling under the Berkel brand. I remember their scale-and-pointer scales from the grocery shop and a hardware shop when I grew up. These scales were also seen on the weekly market in our city. I remember there were also Berkel electronic digital scales using nixie tubes.

This scale has displays on the front (user) side as well as on the back (customer) side, to indicate weight, tare, price per unit and sales price. The displays consist of Panaplex displays. Ranges and price per unit are set through a small keyboard at the user side.

Most of the circuit boards, including the central control logic, and transducer interface circuit, are sitting in a card cage in the heart of the case. Only the display control board is outside the card cage. The boards are interconnected by ribbon cables. When I analysed the boards, I found it was actually using a small computer system for measurement and control, based upon the Rockwell PPS-4/2 4-bit microprocessor.

Several boards are using Rockwell peripheral chips to interface with this CPU. The rest of the logic circuits are CMOS and TTL types. The IC's have manufacturing date codes from 1978 to 1980, dating this scale in about 1980. The weighing principle seems to based upon the vibrating string principle.

When I put this instrument on my kitchen table, it was really looking bad. The keyboard was stuck and filthy. Interestingly, it seemed its last date of callibration (legally required for weighing equipment for commercial purposes) was not so long ago, in 1999. I connected a mains cord and looked what happened. Nothing. I checked the fuses and saw one of the fuse holder caps had disappeared and the mains switch was broken. I bridged the switch, replaced the fuse cap and put a fuse in. Now, to my surprise, the thing seemed to come to life. The displays gave an “All Eights” readout.

When I tapped the keyboard, nothing happened. Putting my hand on the weighing platform, nothing happened. As I didn't have space to keep this Large Object in my home, I decided not to attempt repair, but to salvage the electronics and throw away the rest. Which I did with some regret, as I normally frown upon such cannibalism.

CPU board

The CPU board is located in the card cage. The main components on the CPU board are:

• Rockwell 11660 PPS-4/2 CPU, in a 42 pin QUIP (“spider” package)
• Rockwell 10432 256*4 RAM, QUIP-42
• Rockwell A66T5-11 ROM, QUIP-42
• National LM2900N, DIL-14
• Motorola MC74C907, DIL-14
• RCA CA311, DIL-8
• and a 3.579 MHz quartz crystal.

The board has room reserved for an extra QUIP RAM chip and two 2716 ROM chips in DIL-24 package.

The 11660 is an early PMOS CPU by Rockwell, a lesser known chip manufacturer. Researching for information on Rockwell CPU's, I found references to the Rockwell 4-bit PPS-4 microprocessor (1972) and PPS-8 8-bit CPU (1974). I found a 2-page data sheet for the PPS-4/2 stating its part number 11660. The specified clock frequency is 199 kHz, derived from a directly attached 3.579 MHz TV crystal. There also is a reference to the PPS-4 on the AntiqueTech site on old chips. Except for some applications in calculators, cash registers and pinball machines, the Rockwell CPUs didn't find a very wide acceptance. It seems they made more money by second-sourcing other CPU models such as the MOSTEK 6502, the CPU that powered the Apple-II, Commodore-64 and BBC-B home computers.

Serial interface board

The serial interface board is piggybacked on the CPU board. It is plugged into the CPU bus and has a 10-pin header for connection to something external. The main components on this board are:

• Rockwell 10696 General Purpose I/O, QUIP-42 (“spider” package)
• Motorola MC14411 bit rate generator, DIL-24
• Motorola MCC670, DIL-8
• RCA CDP1854 UART, DIL-40
• CD4011, DIL-14
• CD4049UBE hex inverter buffer/converter, DIL-16
• 2 CD4050AE hex buffer/converter, DIL-16
• 2 CD4502BE strobed hex inverter/buffer, DIL-16
• TI SN75158P dual differential line driver, DIL-8
• and a 1.8432 MHz quartz crystal.

I wonder why they would use 3 separate packages (baudrate generator, UART and a Rockwell GPIO) instead of the single serial interface IC Rockwell offered? Maybe Berkel didn't like the UART belonging to the Rockwell PPS-4 family. Or maybe it was just too expensive or it wasn't at all available at the time this scale was built.

Weighing transducer interface board

The weighing transducer interface board is located in the card cage. The main components on this board are:

• Rockwell 10696 General Purpose I/O circuit, QUIP-42 (“spider” package)
• Some TTL logic circuits
• Some CMOS logical circuits

On the Net, I found a scan of a license by the Spanish government to Berkel to sell the 176SG as a scale for commercial use. This document stated that Berkel used a weight sensor based upon the vibrating string principle. Unfortunately, I am no longer able to check this or analyse the measurement circuitry, as I don't have the weight sensor any more and I didn't pay much attention to it when I took the scale apart.

Display control board

This board contains all the logic to drive the displays and the keyboard. It is mounted vertically in the scale's case. It has 4 connectors:

• On the top (right) side are two ribbon cable headers to connect to the display boards.
• On the bottom are a CPU bus connector and a ribbon cable header to connect tot the keyboard.

The main components on this board are:

• 1 Rockwell 10788 General Purpose Keyboard and display control circuit,
• Some TTL logic circuit,s
• A few CMOS logical circuits,
• tens of MPSA42 transistors as cathode drivers,
• tens of MPSA92 transistors as anode drivers multiplexing the Panaplex displays.

The 10788 contains all the logic circuits for display multiplexing and keyboard scanning. Wonderful. Nevertheless, Berkel needed a bunch of extra chips to do the driving in a proper way.

Display boards

There are two identical display boards, using Panaplex displays by Beckman:

• SP-352 (2 digit) and SP-353 (3-digit) 14 mm displays.
• SP-332 (2-digit) and SP-333 (3-digit) 8 mm displays.

And 8 LEDs (some red, some green) used to indicate functions and error conditions.

Power supply

The power supply board is located in the card cage. It provides a number of voltages (currents are estimates):

• +5V, 2A
• -12V, 1A
• -5V, 100mA, derived from the -12V supply
• 220V DC for the displays, 20-30 mA

The low voltages are fed to the boards through a 10-lead ribbon cable. The 220V DC is fed to the display board by a separate 2-wire cable.

The board is carrying a heat sink on the back, that holds two 3-pin TO-3 voltage regulators: a μA7912 (-12V, 2A) and a LM323 (+5V, 3A). The auxiliary voltage of -5V is regulated by a 2N2905 series transistor and a zener diode.

The 220V DC supply is regulated using a BF259 and a MPSA42. This supply is floating with respect to ground, it is split in -40V and +180V by the display driver board.