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Pocket electronic cipher machine

The HC-520 was a portable electronic cipher machine developed by Hagelin (now: Crypto AG) in Switzerland. It was introduced in 1977 as part of the HC-5xx CRYPTOMATIC family of machines that succeeded the H-4605. The HC-520 and was one of the first fully electronic cipher machines. It resembled a calculator and was small enough to fit inside the pocket of a coat.
The HC-520 looks like an electronic calculator and was considered very compact at the time. It is based around a PDP-8 compatible Intersil IM6100 processor and is powered by a built-in rechargable 6V battery pack. It has a very reliable keyboard with rubber key-tops and produces its output on a custom LCD screen.

It came in two variants: a military version, in a green case, and a civil version in a white (cream) case. Apart from the colour of the case, the machines are identical and both versions are known to have been used by the military.

The HC-520 is extremely easy to operate and came with a plastic instruction card with a flow-chart on either side; one for ciphering and one for deciphering. Both sides can be downloaded below.

The machine shown in the pictures is an early prototype with serial number 43. Judging from the date stamps on the ICs inside the machine, it was developed around 1977 (see below). According to Crypto AG it was sold until 1987. The HC-520 wasn't cheap; in 1977 it had a price tag of 5000 Swiss Francs (approx. 3250 Euros).
Compatible machines
The HC-520 is part of the CRYPTOMATIC family of machines and is compatible with the following family members:
  • HC-520 (Pocket version, resembling a calculator)
  • HC-530 (Suitcase version)
  • HC-550 (Desktop model, based on Siemens T-1000)
  • HC-570 (Desktop model)
  • HC-580 (Desktop model, based on Siemens T-1000)
  • HC-590
The HC-520 contained a (DEC) PDP-8 compatible microprocessor, complete with memory, ROM and various electronic circuits. Nevertheless, it is a very compact machine, which is very unique considering its age. The entire machine consists of a sandwich of three PCBs (Printed Circuit Boards). The one on top of the stack is the keyboard with very robust dome switches.
At the bottom is the processor board with the IM6100, the memory and the backup battery. The middle board contains the display and the rest of the electronics, and is by far the most complex one.

It is clearly visible that the middle board consists of two epoxy PCBs (rigid) with a flexible PCB in between them. This is called a flex-rigid design. The flex part is extended at the left and folded directly into the LCD display. A very unique design feature for the era, which is still in use today.

Just visible in the above image, is the tamper-switch that is fitted to the bottom board. It has a small metal arm that is operated by the only screw that holds the case together. When this screw (located inside the battery compartment) is removed, the entire memory of the HC-520 is wiped, complete with the current key and the message.
The image on the right shows the two main PCBs of the HC-520. The leftmost one is the processor board with the large 40-pin processor at the centre. The RAM-memory is located at the top left (the 6 ICs with the golden caps) and the software is stored in three adjacent ROMs just below the processor.

The processor board connects to the display board (right) with a single-row header. Two I/O expanders (the white chips at the bottom left) are used to connect the processor to the rest of the electronics.

Looking at the date stamps on the various chips, the machine was built around 1977. Particularly important in this respect, is the date stamp on the masked ROM chips (i.e. the chips holding the software). These are custom-built and have to be ordered in large quantities. It is therefore safe to assume that the HC-520 was introduced in 1977.

Click any of the images on this page to enlarge.
The HC-520 with the lid closed The HC-520 with the lid open Close-up of the display and part of the keyboard Sandwich construction of the PCBs The two major PCBs side-by-side Display, lid and the Hagelin logo The HC-520 packed in a black cover The complete package

The HC-520 needs two batteries to operate correctly. One is the backup battery which will be described later. The other one is the battery pack that is fitted just above the display.

Main batteries
Most HC-520 machines were supplied with a rechargeable battery pack consisting of 5 penlight (AA-size) NiCd cells of 1.2V each. This produces a total voltage of 6V. Please note that NiCd cells will gradually degrade over the years so, if you have a working HC-520, you may need to replace the cells. Furthermore, NiCd cells have the tendency to leak if they are not used, which can be potentially hazardous for the interior of the machine.

If you want to use the HC-520 with rechargeable cells, a suitable battery charger should be used. It can be connected to the 9-way D-type connector at the rear of the unit.
The HC-520 can also be used without the batteries. In that case, a suitable PSU (Power Supply Unit) of 6V should be connected to the D-type connector. Only two pins of this connector are used:
  • Pin 1: (positive terminal, +6V)
  • Pin 5: (negative terminal, 0V)
When connecting a power supply, use the above drawing as a guide. It shows the 9-way D-type connector when looking into the socket of the HC-520.

Backup battery
The backup battery is a potential cause of problems. It is a small black unit with 3 Lithium cells inside it. Due to the age of the HC-520, these batteries will be exhausted by now. Like all empty batteries, they may start leaking and could cause permanent damage to the processor board.

It is therefore highly recommended to remove this battery as soon as possible. The HC-520 can operate perfectly well without it. The only purpose of the backup battery is to maintain the message key (and the message) whenever the main battery is flat or being replaced.
The battery pack Another view of the battery pack The backup battery block

Further information

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Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Saturday, 15 January 2011 - 15:15 CET
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