ATtiny servo tester

The reason for making this thing is that one day I found that when the small tester bought by tb was equipped with an MG995 servo, it seemed to keep restarting due to interference from the servo. Although it was later discovered that the Dupont line for the power supply was a bit thin.

The Tiny13A ROM space I use is only 1k. In addition to driving the servo, I also use 595 to control the digital tube display, so the space is quite tight. The compiled size of the firmware is 964 bytes, occupying 94.1%. If I use Tiny85, there will be A lot of surplus.

## Finished product

! [Picture.png]
Due to the implementation of the firmware, the refresh frequency of the digital tube is relatively low. The effect looks OK to the human eye, but it will flicker when taken with a mobile phone. Please refer to the attached video, or watch the video on station b www.bilibili.com /video/BV1qj411D7Ye. It would be a bit prickly to hold it directly on the back, so I 3D printed half of the casing, which is a white circle outside the PCB. Holes were left on the PCB, and three M1 self-tapping screws were used to fix the casing.

The firmware has been tested and is OK, and is in the attachment, in both elf and hex formats. Anyway, this one works for me, but I can’t guarantee that it won’t cause bugs in other people’s hands. So if you want to try it, it is recommended to use tiny85, because the tiny85 has a large space and has an arduino bootloader. Even if the reset cannot be used, you can still download the program. Although tiny13A is not expensive, it will definitely be unpleasant if one is wasted.

## Reset and programming interface:

Because the IO pins are not enough, the function of canceling the reset pin is set in the fuse, and the reset pin is used as a GPIO and connected to the button on the right. When downloading the program using the ISP interface, press and hold the button to let the microcontroller enter the reset state. After downloading the tester's firmware, set the fuse bit and reuse the reset pin. Then you can no longer use ISP programming. If you don't have a serial port bootloader or a high-voltage programmer, this is a one-shot deal.

The ISP programming interface is on the back, using 2x3 patch pins, which facilitates the removal of the pins later:

! [Picture.png]
The VCC and RST on the interface are not connected, so it is marked NC, and programming must be done manually To reset by pressing and holding the button, an external power supply must be provided.

## The microcontroller

is installed under the digital tube, so when welding, it is recommended not to solder the digital tube first, but to test it with it, to avoid disassembling the digital tube if it is welded incorrectly.

## The display

uses a 595 to drive the two-digit digital tube. The decimal point of the digital tube is not used, so the 8th bit of 595 is empty, so it is used to control two transistors to achieve bit selection and switch the display of the digital tube.

## TODO:

I’m too lazy to talk about the details for the moment. Anyway, the circuit is very simple. I will definitely make it up next time [doge]