Tag Archives: #liveupdates

Cloning the ET-3404 6809 adapter for the Heathkit ET-3400

via Dangerous Prototypes

Dr. Scott Baker made the ET-3404 6809 adapter clone:

I’ve become somewhat of a Heathkit ET-3400 enthusiast lately, after building my ETA-3400 memory/io clone. I decided to also clone the ET-3404, which is a 6809 adapter board for the ET-3400. Why? Simply for completeness sake.
The official “experiments” for the ET-3404 aren’t all that exciting, they’re mostly focused around understanding the differences in the microprocessor. Differences such as addressing modes, register changes, etc. There’s not much flashy interfacing like you would find in the other labs. Nevertheless, the ET-3404 fit an important niche in history. Recall that back in the day all of this stuff was new, computers were expensive, and the ability to upgrade your trainer and learn about the 6809 would have been valuable.

Project info at smbaker.com.

Check out the video after the break.

Building a chaotic oscillator from common components

via Dangerous Prototypes

Tim blogged about his chaotic oscillator build:

A chaotic oscillator is an electronic circuit that can exhibit “chaotic“, nonperiodic behavior. A commonly cited example is Chua’s circuit, but there are many others. I always regarded these as carefully designed, rather academic, examples. So I was a bit surprised to observe apparently chaotic behavior in a completely unrelated experiment.

Experimental Zener diode tester

via Dangerous Prototypes

Dilshan has published a new build:

Automatic Zener diode tester is capable of identifying Zener diodes up to 27.5V. Apart from that, it can be used to recognize leads of the diodes/Zeners and detect damaged diodes. This tester is designed using well-known ICs such as MC34063 and PIC16F88.
This unit provides approximately 5% to 15% accurate readings. Based on our observations, the accuracy of this unit can increase by using resistors with 1% tolerance, stable booster circuit, accurate sampling method(s), and with a more optimized PCB layout.

More details on Dilshan Jayakody’s blog. Project files are available on GitHub.

App note: Battery Fuel Gauging LSI [Smart LiB Gauge] for 1-Cell Lithium-ion/Polymer with LC709204F

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App note from ON Semiconductor on their Smart Fuel gauge LC709204F. Link here (PDF)

LC709204F is a Fuel Gauge for 1−Cell Lithium−ion/ Polymer batteries. It is a part of our Smart LiB Gauge family of Fuel Gauges which measure the battery RSOC (Relative State Of Charge) using its unique algorithm called HG−CVR2. The HG−CVR2 algorithm provides accurate RSOC information even under unstable conditions (e.g. changes of battery; temperature, loading, aging and self−discharge).

Bus Pirate “Ultra” HDL moves from simulation to real hardware

via Dangerous Prototypes

Latest simulation of Bus Pirate Ultra HDL

The HDL is complete enough to start testing on real hardware. This update puts almost every feature under control of the state machine in the FPGA so commands can be pipelined with repeatable precision. Commands (write/read SPI, set/clear pin, measure voltage, update PWM, enable pull-up resistors, etc) are pushed into a FIFO buffer using a 17bit command/data protocol inspired by the interface of ST7789-based LCDs. When the state machine is enabled the commands are processed in one continuous stream.

Verilog HDL for the FPGA is on github, the latest updates are currently on the command-data-refactor branch. A synthesized version of the bitstream is in the forum.

giggiu16 has already build a v1d. There are a few more boards to give away, if you’d like one please message Ian in the forum.

Bus Pirate Ultra 2.8 inch display and the danger of Taobao suppliers

via Dangerous Prototypes

We’ve been prototyping the Bus Pirate Ultra with a 240 x 320 pixel 2 inch LCD, but it’s just a bit small and hard to read from a distance. A 2.8 inch version is available that fits the full width of the Bus Pirate PCB, with the trade off of bigger pixels/lower pixel density. We bought a few displays from various “manufacturers” on Taobao and made up a daughterboard. It failed spectacularly because the datasheet was so wrong!

Anode and cathode pin locations in the “datasheet”
Anode and cathode position on the actual display

We don’t have to go beyond pin 1 to find a major and obvious error. The datasheet lists pin 1 as the LED backlight anode, and pins 2-5 as the cathode. The printing on the flex connector makes it clear that four cathodes (K1-4) join into a single trace to pin 1. A single anode (A) trace connects to four pads on the connector (pins 2-5). The backlight connections are backwards.

Coincidentally, datasheets for other similar displays (2.8 inch, 50 pin connector) match the corrected pinout. This datasheet just had it backwards. We reversed the backlight power and ground on the PCB by drilling out a trace and creating some strategic solder bridges. While the LEDs light, the display doesn’t respond to any commands so other connections could be wrong.

That’s not all. The flex cable is actually several millimeters shorter than listed in the datasheet, so it can’t reach the connector through the slot in the daughterboard.

We had similar issues with this supplier’s 2 inch display. The dimensions in the datasheet are a bit off, and their sample initialization code doesn’t work. We asked for an updated datasheet and received three different versions, none of which matched the actual display.

Their Taobao page has pictures of a factory and a nice section on after sales support. A charitable guess is that they manufacture runs of custom displays, and sell the excess on Taobao. That would explain all the different datasheets they so readily have available. We tried to get another grab-bag of PDFs for the 2.8 inch display, one of which might match the actual pinout, but at this point they got tired and ghosted us.

Will we stop buying prototyping samples on Taobao and 1688? Definitely not! It’s a great way to see what’s a cheap commodity product. This process plays out in the Shenzhen markets as well, people sell a lot of stuff without knowing exactly what it is. It’s kind of up to us to know what we’re buying, and sometimes it’s a crapshoot. When we find a sample we like, it’s time to send someone up to the factory to meet the boss, drink way too much tea, and ensure we’ll have a steady and consistent supply in the future.