Summary of USB PCB Business Card Using ATtiny85 Microcontroller
This USB business card uses an ATtiny85 running V-USB to emulate a keyboard and type text when plugged in; typing triggers when the CAPS LOCK LED is toggled three times. The design follows V-USB recommended circuitry and focuses on a compact PCB made in CadSoft EAGLE with surface-mount parts and in-circuit programming pads.
Parts used in the ATtiny85 USB PCB Business Card:
- ATtiny85 microcontroller (SOIC package)
- USB connector (USB plug)
- Two 68 ohm resistors (for USB data lines)
- 1.8 kilo ohm resistor (pull for D+)
- Two 3.6V Zener diodes (data line clamping, Mini MELF)
- 0.1 uF decoupling capacitor (between 5V and GND)
- Surface-mount pads (0604 package for most components)
- PCB with exposed SCK and MOSI pads on USB connector
- Two programming pads for MISO and RESET (for ISP)
This is a business card that will type out some text when you plug it into a USB port. It uses a ATtiny85 microcontroller with V-USB based code to emulate a keyboard. The typing is triggered by the CAPS LOCK status LEDs being toggled 3 times.
This instructable will focus on using CadSoft EAGLE to create your own USB PCB business card. I want you to be creative in the design, so some minor steps I’ve taken may have been omitted.
Code download is provided on step 8.
Step 1: Circuit
The circuit is based on V-USB’s recommended circuitry. It’s powered by the 5V from the USB port. There’s two 68 ohm resistors, one on each of the USB data lines, these act as terminating resistors which suppress reflected signals. There is a 1.8 kilo ohm resistor on the D+ line, which allows the computer to detect when something connects to the USB port, and it identifies the device as a low speed device. Two Zener diodes with Vz of 3.6V are on the data lines to clamp the voltage on those lines. There is a 0.1 uF capacitor between the 5V and GND as a decoupling capacitor.
Since the business card should be a compact and thin design, 0604 surface mount packaging is selected for most of the components. The diodes are Mini MELF packaging (they look cool in my opinion).
The microcontroller is an ATtiny85, which is a 8 pin AVR microcontroller. The SOIC package version is chosen to keep the design compact and thin.
To program the microcontroller, in-circuit serial programming is used, which requires the signals: reset, SCK, MOSI, MISO, along with power and ground. The SCK and MOSI are exposed by the USB connector, while two pads are provided for the MISO and reset signals. This allows for a programming adapter to be made.
For more Detail: Using ATtiny85 Microcontroller USB PCB Business Card
- How does the business card trigger typing?
Typing is triggered when the CAPS LOCK status LEDs are toggled three times. - What microcontroller is used in the project?
The project uses an ATtiny85 microcontroller in an SOIC package. - What USB interface code is used to emulate a keyboard?
The project uses V-USB based code to emulate a keyboard. - How is the USB device identified as low speed?
A 1.8 kilo ohm resistor on the D+ line allows the computer to detect a connection and identifies the device as low speed. - What components protect and condition the USB data lines?
Two 68 ohm terminating resistors and two 3.6V Zener diodes clamp and suppress signals on the data lines. - What decoupling is provided for power stability?
A 0.1 uF capacitor is placed between 5V and GND as a decoupling capacitor. - What packaging is chosen for compactness?
Most components use 0604 surface-mount packaging and the Zener diodes use Mini MELF; the ATtiny85 uses the SOIC package. - How is the ATtiny85 programmed on the assembled card?
In-circuit serial programming is used with exposed SCK and MOSI via the USB connector and two pads for MISO and RESET.
