Calculators of the past

This page has is a great resource for information about calculators from long ago. In particular the section on the Anita desktop calulator is interesting to me using vacuum tubes, cold cathode tubes, nixies and a dekatron.

Count register

This circuit is a synchronous binary decade counter using relays. It counts from 0-9 and back to 0 again. Its based on my design as demonstrated in this video. It is used to count the pulses that come from the telephone dial numeric input device. It also counts up during the square root process in order to work out each digit of the square root as calculations take place. It acts as an input to the AE register LSB and gets shifted in as necessary.

Designing a synchronous decade counter which only uses 12 relays for 4 bits was a bit tricky. K-maps gave me terms which were not very easy to cram into the limited number of contacts. Therefore I took the approach of computing a change, no-change signal for each digit which gets propgated down the chain. Then there is some logic to disable this and reset the whole counter when the count gets clocked beyond 9. The circuit also generates an =9 signal for determining when to move on during the calculation of square roots and also generates the subtractor signals SUB1X2 and SUB123 which are needed for 9s complement formation.

Once again this circuit makes use of the edge triggered D-type flip flop I posted about previously. The diodes are used mostly for OR gates, but some are protecting the circuit from the internal operations of the flip flops (isolation diodes).

Also included in this circuit is the telephone dial pulse inverter, and a monostable circuit which generates a short clock pulse to load the dialed number into the AE reg during data entry. This takes advantage of the dial rotation contacts on the phone dial which are closed for the whole rotation of the dial and open to indicate the dial returned to rest.

Count Register

Answer/entry register and display driver

I have been progressing with the relay square root machine project. I have finished the schematic capture for the answer and entry register which also acts as a display driver and drives a bank of 8 nixie tubes. This circuit is a shift register which accepts the users input of a floating point number entered via the phone dial interface. It also acts as an answer register to display the final result. You can see a video of the first test of this working here.

The AE register circuit needs to store 8 digits of binary coded decimal information. It also decodes these to drive the 10 cathodes of the nixie tubes. There is a ripple blanking signal to suppress leading zeros and this is also affected by the decimal point position. It also has to include a multiply by 5 operation during transfer into the accumulator which requires a little extra logic. Also there is an extra set of signals which are generated for the input to the subtractor as part of forming the 9s complement of the number. There is also a test for AE=0 which is used by the central control logic. All the latches are built up using the basic D-type relay flip flop unit. The advantage of edge triggering is that fewer relays are used and only a single clock line is needed. The shift input to the AE reg LSB digit comes from the C register and dial counter.

 

Generic D-type edge triggered flip flop with asynchronous set/reset

Answer/Entry Register

Answer/Entry Register (MSB)

Answer/Entry Register (LSB)

Answer/Entry Register and Display

I used EAGLE for the schematic capture but it does not support hierarchical schematic sheets. So therefore since I am not really using this to build circuit boards, I faked it by making components which look like the interfaces to other sheets. Really all I am only trying to do is generate a circuit diagram for documentation.

More augmented reality info

Top AR trends

AR eye glasses

Cool looking wearable monitor glasses.

And another set from Sony.

AR from Sekai Camera

This post describes a company in Japan doing some interesting AR work.

Robot toys as part of structured gaming

This article describes how robotic toys are often forgotten, but may become more compelling if linked as avatars to some form of online gaming.

Relay computer enclosure

I decided that my carpentry skills are not up to the task of making something really nice yet, so I decided to engage Matthew Richter of XOMOnline to build the cabinet. I think Matthew’s style is prefectly fitting to the feel that I am going for and the 1940s technogy, and I’m sure the results will be beautiful.

Hop over walls!

Here is a nice jumping wheeled military robot that is able to hop over walls.

AR display on a contact lens

University of Washington researchers are developing a heads up display on a contact lens.