Mainly there are three things. First the motor driver with a PWM and a readback with a light barrier. Second the thermoelement with the shift register and the write enable. Third the catirge detection with 3 pins.
A simple PWM regulated by the light barrier to have a controlled printing speed. The measurement shows, that the light barrier is regulated to 220Hz. The PWM has a main frequenzy of 15kHz and has a hold time around 25%. This will be differen for different tapes and devices, because it is regulated. To move after printing it has a hold time of around 75% with the light barrier at 440Hz.
4 Pins are used for generating the image
- clock (2MHz)
- Data (changing on falling edge, latched on rising edge)
- _Latch (short low pulse to latch the data)
- _Strobe (to enable the heater 3.15ms at my printer)
The data could be clocked in when ever you want. Set _Latch to low will transfer the register content to the heater. There are 12 Byte with 8 bit = 96 pixel to be set. It will be done twice with the even bits and the odd bits directly after each other with its own strobe. The last bits for the bottom and the first Bits for the top. That mean 96 pixel for 18mm, 84 pixel for 12mm and xx pixel for 6mm. Every fourth light barrier pulse two 3.2ms heats are applied.
There are 3 Pins. Two for tape type and one for tape insertion. Low means pin is pressed.
| Pin | Level | Result |
|---|---|---|
| TD | high | no tape |
| TD | low | no tape |
| T1 | high | 6 mm |
| T1 | low | 12 mm |
| T2 | high | 12 mm |
| T2 | low* | 18 mm |
* needs also T1 low
After 4 rising edges the original is printing (heating) 150 pulses (4*150) result in 18.5mm print length. That result in a horizontal resolution for every edge 18.5 mm / 600 pulses = 0.031 mm/pulse = 3/100 mm / pulse. I think the heating capacity holds the temp that long, that this resolution could not be reached. This result in 0.124mm/4pulse. So I start with this 4 pulses like the original. 220 Hz result in 6.6mm/s.
Vertical we have 96 bits on 12mm = 0.125mm/bit.
So hope I have a calculation error and the resolution is horizontal and vertical identical.
The programm uses 37828 byte RAM from 532480, with only one buffer for the 12 Bytes. Let`s assume, that 400000 are free at the end, when all is programmed. 400.000 / 12 = 33333 lines are possible to store. 33333 * 0.125mm/pulse = 4166 mm. 4m? Who will print that? That mean the memory is quite enough for that. Go the way round. 25cm is a long text for such a lable. 250mm/0.125mm/pulse = 2000 pulses. 12 Bytes * 2000 = 24000 Bytes. So I will reserve a Buffer of 32k.
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Batteries are not enought with this solution and anyway the place is needed for the ESP32 I use a 9V Power supply directly soldered on the smal power PCB (no image yet)
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Remove the micro controller. Okay, now the display and the keyboard is not working anymore. But when you print from your PC, there is no need anymore.
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R8 from the µC side need to be tied to GND. Could be made switchable, but not needed.
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C25 need to be increased by a parallel 1nF. Whithout that I had a lot of glitches.
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R9 need to be removed. The replacment is a 10k resistor on the µC Side to 3V3 from the ESP32
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Between this resistor and the C25 is now the lightbarrier signal of the transport motor
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5V enable need to be connected on (you find it inside of the not existing IC, the smal bridge)
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PIN 2-5 (Latch, Clock, Heat and Data) need to be connected to 15, 0, 17 and 4
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PWM need to be connected on R6 (the side, which is not connected to R7)
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A step down from 9V to 5V is needed to feed the ESP32 on the 5V side. The 5V from the main pcb is to weak to feed the ESP32 with W-LAN
There are some recordings of the original signals in the folder pcb_details
Pictures:
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Copyright (c) 2025 Christian Oelschlegel
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