This project is based on the 1975 Bell & Howell IMD-202 digital multimeter reconstructed project, which reuses the original digital tube display, power supply, and housing. In order to achieve new features, AVR-based wired control panels are integrated on the original PCB, and two digit row switches are installed in the chassis, 8 to the rotary switch and panel mounting buttons, and written graphics to panels.
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This project has highlighted a few things I like, such as representatives.
I started from D & D (Dungeon & Dragons) since 1978. Therefore, the project name is 1978, which is based on the RESTO-MOD building based on user interface technology based on the same time. Be
Repeating the old parts and technology is very interesting, in addition to "doing the right thing" because of the reasons we already know, we also need to disassemble and reverse engineering. Decompose things and figure out how they work, this is very interesting. In this process, I often learn what applies to other projects.
Unless there is a microcontroller and some software that can be written, downloaded, debugged, and iterative, the project will not be interesting.
I like old display technology, classic panel mount switch / knob / button, "laboratory equipment" blue and sheet metal shells. I greatly appreciate the 74xx series logic IC and PCBs on the PCB. They simplify the tools / skills required for reverse engineering, hardware prototypes, and do this. I often use the old 8-bit processor (Z80, 8051, 8088, 6502, 6805, 68HC11, 68K). In the past, I wrote C and assembly code for all of these processors. However, I am not an outdated software development environment and the loyal supporter of the code library, nor is it a lot of time to integrate the old tool chain with modern IDE. I prefer to keep synchronization with software development and make it applicable to the current job market.
A few days ago I saw someone published commentary that the digital tube "is now very bored", there is nothing to achieve cool ideas. I disagree. The digital tube is still cool. In addition to displaying the time in the day, we only need to find new applications.
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The project in this article uses the Bell & Howell IMD-202-2 million table. This device is part of the electronic course of the DEVRY University of the 1970s. If I understand it correctly, this multimeter is a project built by students. This design is based on the Heathkit IM-12120 meter. Obviously, Bell & Howell obtained the right to re-create the design in different shape sizes and housings. These multimeters are produced in large quantities.
Even if you may put one at home, or you can easily buy it on e-commerce websites like Taobao, if you have a little patience, you can even buy them cheaply. Cheap, I mean is very cheap, a pair of digital tubes, a pair of 7441 drivers them, and provides 170V for the tube and provides 5V for your custom electronic device / microcontroller.
I have selected Attiny88 AVR microcontroller for this project. This controller is integrated with flash, SRAM, reset logic, integrated oscillator, and the like. When using these parts, I feel like cheating. My controller is just a 28-pin DIP outlet, some wires and 4 connectors. Power-on reset does not have an RC circuit, no crystal and capacitance, no external bus logic, no external pull-up resistor. These AVR controllers simplify integration with the original 7400 series logic IC. There are some limits, such as the original 74xx and 74LSXX outputs that cannot be reliably driven the AVR input logic level. However, this is not a problem for the project.
I have built the initial version of the project to prove this concept. It works well, and it has been placed on the shelf with other classic D & D dice tower, which can be used regularly on the game.
Hand-constructed controller board with processor is integrated with the original PCB and power supplies in the Bell & Howell Multimeter. To simplify integration, I simply delete two DIP sockets directly connected to the 7441 NiXie decoder / drive, and insert my custom panel into it. Be
The socket provides + 5V, GND, and two 4-bit BCD interface to power the control board and drive the display. Be
The remaining only the old switches and banana plugs, welding new panels, install new switches, connect them to the controller board, write some simple code, and apply new graphics. In this case, I use 8 to select the dice type, use the two-digit gear switch to select the number of dice, and use the square panel to install the button. The software is developed from scratch using free Atmel Studio 7.0 IDE and toolchain.
I have more hardware to build four, and I plan to build more hardware by additional features. I will record these buildings and record them as new projects. Plan function update includes simplified switches installation (released panels), speakers, PCM sound, limited speech synthesis, rotary encoders, additional output (LED), etc. for user input.
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Article Source HackADAY
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