Texas TI-1025 Calculator

This calculator was a gift from a seller after bying him a few other Texas machines.

It works, but the VFD is barely visible under normal ambient light conditions.

This VFD is a SIPBentPin package, 8-digit 7-segment with DP vacuum fluorescent display and looks like a Itron FG85C1, whose main specs are:

• Nominal supply voltage:  24VDC 
• Maximum current/segment:  0.07mA 
• 19 pins package
• 2.188"L x 0.788" high.
• Made in Japan.

The SoC is a 28-pin DIP IC Texas TMC0923NL, made in 1979 week 14, in Singapura.


The 9V battery from the power supply is not enough to feed the VFD, as it requires a nominal 24VDC to give an acceptable brightness.

Texas have employed a brilliant idea to generate the required high voltage without involving costly  DC-DC converters: A simple voltage multiplier using a few diodes and ceramic capacitors where the input AC voltage is coming from the SoC itself.

In my calculator, the VFD high voltage has about -22.5VDC with a input 54KHz AC voltage of 3VAC coming from pin 26 of the SoC. 
The VFD high voltage was measured between pin 1 (+9Vbatt) and pin 27 of the SoC.



Filament in red color...

Current consumption after power ON, single zero digit lit: 14mA

All digits lit: 15mA

 

Texas TI-37 Galaxy Solar

Vintage radioactive wrist watches

Vintage watches from the 1910-1920 era could use a paint based on radioactive material like Radium to excite another fluorescent material in order to emit light.

This paint was used on watches hands and dials like this one:

Building a Geiger counter based on a SBM-20 GM tube and a popular arduino project:

Testing the Radium from the watches hands - 6798CPM and counting...

Slightly radioactive CRT:

The NP-25 Nonpariel Physical calculator project, by Chris Chung

Github open source code

Based on the Eric Smith's Nonpareil simulator project.

Available ready built or in kit form from Chris Chung.

This is a neat scientific calculator machine, sporting as many features as you can find on the vintage famous HP-25 calculator series of the 70's, and a few more options thanks to the improved modern hardware used in this project. Besides the HP-25, it has the capability to support more HP Woodstock and Spice series calculators.

It is based on a MSP430G2553 micro-controller to emulate the real original HP-25 series calculators by running a customized firmware developed by Chris, based on the smart simulation code developed by Eric Smith which in fact run the original calculator microcode.

 

Some of the Kit builders pictures

 

Iceman from MoHPC:

 

 

My onwn build

 

Passive components installed in the lower side of the PCB.
On the original project, it are mounted in upper side.

By moving the passive components to the lower side, the front is less cluttered.