RetroBlinkEnglish
project overview  | |
| |
| Year | 2022, 2025 |
| Number of pixels | 25 |
| Grayscales / Colors | 2 |
| Illuminant | 5mm LEDs |
| Power input | |
| Contact person | Arne Rossius |
| Project website | |
RetroBlink is a version of MaxiBlink without ICs. It also changes the matrix size from 4x6 to 5x5, and uses diagonal lines for both "rows" and "columns" to get a different look for the patterns.
Mode of Operation
The operation is based on a 10 bit Maximum Length Sequence shift register, built from flip-flop stages using 2 transistors each. Each stage is coupled to the output of the previous one, so it switches to the previous stage's value when a clock pulse is applied. The first stage is driven by an XOR gate which combines the signals from the outputs selected for the feedback (see link above). To reduce the number of transistors required, the feedback uses only 2 outputs, so the XOR gate only needs 2 transistors with a 3rd transistor added to generate the complement signal required to drive the flip-flop.
The flip-flop transistors drive the LED matrix directly, so there are 5 stages using NPN transistors to drive the cathodes lines, and 5 stages using PNP transistors driving the anode lines. This mix of transistor types requires the oscillator to provide both negative pulses (to drive the NPN stages) and positive pulses (to drive the PNP stages) at exactly the same time. A simple design with only 2 transistors was sufficient for this. The speed of the oscillator, and thus the duration each pattern is shown, can be adjusted with a potentiometer in the oscillator circuit.
As the flip-flop stages are unevenly loaded with one side driving the LEDs, they tend to switch to the side without load at power-on. As the LEDs are alternately connected to the true and complementary outputs of the stages, this ensures the shift register doesn't turn on with all stages set to "zero" (complementary output active), which would prevent the circuit from starting up (and which has been a problem in the MaxiBlink design).
Hardware
Version 1.0
Version 1.0 was only built as a prototype on perfboard, using rectangular LEDs.
- Schematic diagram (PNG)
Version 2.0
In this version, a proper PCB was designed, which allowed the flip-flop circuits to be moved in-between the LEDs, making the board a lot smaller. The values of some passive components were changed to more common ones, and the circuit was optimised to require as few diffenent resistor values as possible.
The LED current limiting resistors are shown without a value in the schematic; the kits use 1 kΩ which works with most high-brightness LEDs, but for low efficienty types (especially yellow-green LEDs) they can be reduced. They shouldn't be much lower than 270 Ω to avoid overloading the transistors, which could stop the flip-flops from toggling reliably.
Enclosure
This is a design for a front cover, which can be 3D printed and screwed to the PCB. It requires a diffusor sheet for best effect, which could be a sheet of paper, or a more advanced material such as a #225 "Neutral Density Frost" stage lighting filter sheet. There is also an optional bottom cover (tray) to protect the underside of the PCB from being shorted by metal objects.
- All parts (OpenSCAD code)
- Front cover (STL file) - print in white
- Front cover lid (STL file) - print in black, clips onto the front cover
- Rear cover (tray) (STL file) - optional