Old calculators
26.01.2008 11:52
My grandfather gave me two old calculators a while ago. Now I've finally found some time to have a close look at them.
First one is TRS 529, made by Tvornica računskih strojeva Zagreb (I wonder if the same acronym as Tandy/RadioShack is a coincidence). As you can see from the photo it's a scientific calculator with basic trigonometric functions and memory for one variable.
A look inside reveals a tiny vacuum fluorescent display powered by an early DC-DC converter made by Ematron Inc., Taiwan. This hybrid circuit converts +6V from four AA batteries to -25V which is then used as anode voltage for the display and also for powering the processor. CPU is Rockwell A4001CC inside a plastic staggered dual in-line package. 7801 says that it's been manufactured in the first week of 1978.
Sadly it doesn't work anymore. As far as I can see the power supply works correctly, however the CPU appears to be completely dead. When I connected it to an oscilloscope I could see no attempts at keyboard scanning or display multiplex.
The other calculator is Hewlett Packard 21. It's the first RPN calculator I've seen. I remember it as the calculator that had the "Enter" key like the big computers and that only my grandfather knew how to use.
From the technical standpoint there is little I could add to information that is already available on the internet. This one did show some signs of life when powered up. The little LED display shows "0 0", however it appears there is something wrong with the keyboard, since only the top row of keys produces any response.
I didn't try to open it to see what's wrong since at first I didn't see any obvious way of taking it apart. Now that I know that you have peel away the front two rubber legs I'll probably look into it.
