I am very lucky to have a son in the Dental Equipment Service Business who faithfully watches for circuit boards that he can salvage from discarded equipment and deliver to the old man (me). Here is the cache that I got on Friday.
Sometimes I will just salvage them out for the parts but I am always watching for interesting assemblies that I can add to my resources and repurpose. Among the boards were 2 sets of (11) lighted momentary push button switches. These switch banks came from a European Panoramic X-ray machine as many of the parts were made by Siemens. I believe they were used to select the intensity of the x-ray exposure. Obviously heavier people require a more powerful x-ray to penetrate teeth and bone than does a small boned person.
Here is one bank of the switches mounted to its original board. I decided to take the other bank of switches and see if I could independently power it on a bread board. I wanted to see if I could get the buttons to sequence properly and I wanted to see what kind of output I could generate.
The main chips on the board are SAS580 and SAS590 by Siemens Electric. I could not find data sheets or information on these chips at first so when I powered them with 5 volts nothing worked. After more searching on the internet I was able to see some information in the google images page. From the images and sample schematics I learned that 30 volts was a more typical voltage for these chips and so I cranked the power supply up to 20 volts and the switch bank came to life.
I could now push the buttons at random and the LED in the corresponding button would light. My next experiment was to see how the different buttons would affect the output. There were only 9 pins going into this board and so I set up a chart and measured each pin as individual buttons were pressed. I also looked at the different pins with the scope. I suspected the output would either be analog and be a voltage change on a pin or series of pins or it might be digital and show up as a binary sequence on a series of pins or even as a PWM modulated output. The scope saw only DC voltages regardless of which button was pushed and in the final analysis only one pin (#5) was showing any change from button to button. The output was apparently analog on pin 5. The output had a direct relation to the voltage that I was supplying to the board for the Vcc.
I set the voltage to 20 volts for the Vcc and here is the output sequence that I got off pin 5:
Button Pin 5 Voltage
1 0.45V
2 6.24V
3 6.43V
4 6.62V
5 6.81V
6 6.99V
7 7.18V
8 7.36V
9 7.54V
10 7.72V
11 7.91V
These voltage differences could easily be interpreted by the Analog ADC inputs of an Arduino or other micro processor. This board will be able to be repurposed if the old man is able to come up with an idea and a practical purpose. The buttons are mutually exclusive so one is not able to select more than one at a time. This limits the new application to some extent. I have a set of toggle switches by the bench that I use to turn on and off lights and different sections of the lab. This was my first thought but I always have multiple lights and sections selected. Time will tell and just to make it easier in the future I will document what I have learned and put it on a tag so that when the day does come I do not have to figure it out again.
Here is a short video demonstrating how the switch bank works.
I hope you are all well and finding things to keep you busy. Thanks for checking out my adventure with the switch bank.
John
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