ESP8266 Community Forum

- Sat Jan 25, 2020 5:37 pm #85408 The upload issue when strobe is connected is slightly strange.

GPIO15 must be low at start up both for normal operation or for serial uploading. I could understand it if some leakage current from strobe was causing that not to be the case as the pull down resistor on the NodeMCU board is 12K which is a bit high to give a solid pull down and that could be cured by putting an external additional pull down on that line e.g. 2k2. I would do that anyway to make sure it is starting up correctly.

However, if that was the case it would also be preventing normal operation as well as uploading.

You do need to disconnect busy for uploading in that wiring scheme as otherwise the RX pin won't be able to get the serial data from the usb serial interface. You could avoid that issue by swapping GPIO3 (RXD) for one of the data lines in the assignment.

If you are getting garbled output the first thing to check is that the data lines do correspond exactly.

- Wed Feb 12, 2020 3:03 am #85613 I now have 74HC595 shift register's, can they help with the problem? The wires seems to be right.

- Thu Feb 13, 2020 6:23 am #85644 It is possible that your problem is with the logic voltage levels. As said earlier the printer interface uses 5V levels and the nodemcu is giving 3.3V levels. A lot of the time this would work but if the interface is picky then you would need to use level shifters for the data lines and strobe.

The shift registers can help reduce the number of GPIO lines needed by using a 1 GPIO to feed the input to the shift register and another to clock it. After the 8 bits have been clocked in then you then send a strobe.

The 74HC595 won't directly help with the level shifting but could be used to simplify this by running the shift registers from 5V so the output levels are good and then using just 3 level shifters to drive the shift register data and clock lines plus the strobe.

- Mon Feb 17, 2020 6:36 pm #85707 Hello,

i have use the register for the exstra pins, i found out a wire that i had solder to the interface was broken off. After reconnecting it works.

Now i'm building the ticket but when i print it seems to be off, even after a press on the reset button of the nodemcu the ticket is diferent.



This photo is 2 times the same code with only a reset press between them. The fontsize is wrong, some items did not write or miss some characters and the ! in the - line are not written in the program.