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Got a couple of additions to the junk inventory this weekend, a dead Dell Insprion 1100 and a defunct HP Laserjet 4. The touchpad in the laptop and the VFD board in the printer caught my eye, so I decided to see if I could get them to be friends...
The only chip I'm using on the breadboard is the Atmel AVR microcontroller in the center, the rest of the parts are leftover from testing my stepper driven Etch-A-Sketch project.
Turns out that most Synaptic Touchpads used in laptops communicate via the standard PS2 protocol, using the same wiring scheme as a conventional mouse and keyboard. The pad could probably be wired to a pc and operate as a mouse without any special drivers. But as PS2 is not a common protocol used in microcontroller applications, I had to write my own interface code for the Atmel 8535 AVR I planned on using. Fortunately, the PS2 protocol is not that complex, and references describing it are easily located on the net. Synaptics also has a very good interfacing document available for download that details the electrical interface and the commands used to control the device.
Here's the connections on the back of the touchpad (pins functions in pairs):
The VFD control panel turned out to be a bit more elusive, but after some detective work with a multimeter and the datasheets from the chips on the board I was able to determine how it operates. It's actually a great little board with a nice 16 char VFD, 3 programmable leds and 8 buttons - it makes a great testbed tool and requires only a single +5V supply. The VFD is also a nice change from boring everyday lcd displays (it's the tubes, man
).
Here's the VFD board displaying the coordinates of the touchpad:
While working on this project I wondered if I could get the pad to operate like a qWheel type of device, like used on the iPods. Well,a little bit of geometry math coding later and tada, rotary encoder emulation.
Here's the VFD displaying a bargraph indicating input from circular motion on the pad:
This feature and the ability to devide the pad into multiple zones makes it a great input device for projects. Uses can be fan speed controllers, light dimmers, etc.; the possibilities are endless!
It turns out that the touchpads and this model VFD board are available and inexpensive in the surplus market or eBay, making them great experimenter devices. Unfortunately, neither will natively hook to a pc through parallel or serial interfaces, so a microcontroller has to be used. However, if the interest level in a project using these is there, I might design and offer inexpensive interface boards that would translate the PS2 to RS232 or similar.
Here are some resources I used for this project, as well as the source code I wrote that is well commented and contains additional technical information:
Synaptics Developer Resources - Interfacing Guide available here
Mitsubishi M66004M VFD datasheet (pdf)
PS2 protocol
My source code
The only chip I'm using on the breadboard is the Atmel AVR microcontroller in the center, the rest of the parts are leftover from testing my stepper driven Etch-A-Sketch project.
Turns out that most Synaptic Touchpads used in laptops communicate via the standard PS2 protocol, using the same wiring scheme as a conventional mouse and keyboard. The pad could probably be wired to a pc and operate as a mouse without any special drivers. But as PS2 is not a common protocol used in microcontroller applications, I had to write my own interface code for the Atmel 8535 AVR I planned on using. Fortunately, the PS2 protocol is not that complex, and references describing it are easily located on the net. Synaptics also has a very good interfacing document available for download that details the electrical interface and the commands used to control the device.
Here's the connections on the back of the touchpad (pins functions in pairs):
The VFD control panel turned out to be a bit more elusive, but after some detective work with a multimeter and the datasheets from the chips on the board I was able to determine how it operates. It's actually a great little board with a nice 16 char VFD, 3 programmable leds and 8 buttons - it makes a great testbed tool and requires only a single +5V supply. The VFD is also a nice change from boring everyday lcd displays (it's the tubes, man
).Here's the VFD board displaying the coordinates of the touchpad:
While working on this project I wondered if I could get the pad to operate like a qWheel type of device, like used on the iPods. Well,a little bit of geometry math coding later and tada, rotary encoder emulation.
Here's the VFD displaying a bargraph indicating input from circular motion on the pad:
This feature and the ability to devide the pad into multiple zones makes it a great input device for projects. Uses can be fan speed controllers, light dimmers, etc.; the possibilities are endless!
It turns out that the touchpads and this model VFD board are available and inexpensive in the surplus market or eBay, making them great experimenter devices. Unfortunately, neither will natively hook to a pc through parallel or serial interfaces, so a microcontroller has to be used. However, if the interest level in a project using these is there, I might design and offer inexpensive interface boards that would translate the PS2 to RS232 or similar.
Here are some resources I used for this project, as well as the source code I wrote that is well commented and contains additional technical information:
Synaptics Developer Resources - Interfacing Guide available here
Mitsubishi M66004M VFD datasheet (pdf)
PS2 protocol
My source code