7/06/2011 Your snapshot on a thermal printed receipt, instantly!

What could be better than a low-res black and white photograph printed instantly on paper that will yellow and crumple over time? Wow, we really need to work on our sales pitch. But all kidding aside, we love the idea that [Niklas Roy] came up with in order to build this thermal printing camera.


His Picasa album has two snapshots of the hardware. He’s using an LM1881 for video sync separation just like he did with his PING project. From there an ATmega8 microcontroller grabs each column from the image and prints it using the thermal printer. It looks like everything runs on a 9V battery which is nice for portability (although we still never got our hands on that rechargeable 9V we’ve been meaning to pick up). Perhaps just as impressive is that [Niklas] got this up and running with about 400 lines of code. Nice!
Of course you’ll want to see this in action so we’ve placed a video clip after the break. Just like old-timey cameras it looks like you’re going to need to sit still until the image is done printing.

Essential mechanisms

A thermal printer comprises these key components:

• Thermal head — generates heat; prints on paper
• Platen — a rubber roller that feeds paper
• Spring — applies pressure to the thermal head, causing it to contact the thermo-sensitive paper
• Controller boards — for controlling the mechanism

In order to print, thermo-sensitive paper is inserted between the thermal head and the platen. The printer sends an electrical current to the heating elements of the thermal head, which generate heat. The heat activates the thermo-sensitive coloring layer of the thermo-sensitive paper, which changes color where heated. Such a printing mechanism is known as a thermal system or direct system. The heating elements are usually arranged as a matrix of small closely-spaced dots—thermal printers are actually dot-matrix printers, though they are not so called.

The paper is impregnated with a solid-state mixture of a dye and a suitable matrix; a combination of a fluoran leuco dye and an octadecylphosphonic acid is an example. When the matrix is heated above its melting point, the dye reacts with the acid, shifts to its colored form, and the changed form is then conserved in metastable state when the matrix solidifies back quickly enough. See thermochromism.

Controller boards are embedded with firmware to manage the thermal printer mechanisms. The Firmware can manage multiple bar code types, graphics and logos. They enable the user to choose between different resident fonts (also including Asian fonts) and character sizes.

Controller boards can drive various sensors such as paper low, paper out, door open, top of form etc., and they are available with a variety of interfaces, such as RS-232,parallel, USB and wireless. For point of sale application some boards can also control the cash drawer.

Applications

Thermal printers print more quietly and usually faster than impact dot matrix printers. They are also smaller, lighter and consume less power, making them ideal for portable and retail applications. Cost of thermal paper, their only consumable, was somewhat less than US$0.10 per sheet as of 2010.^[2] By comparison, one study of the per page cost of color inkjet printers  found cost of third-party ink cartridge and paper to be about $0.05 per page (some low-capacity cartridges are more expensive to use). Roll-based printers can be rapidly refilled. Commercial applications of thermal printers include filling station pumps, information kiosks, point of sale systems, voucher printers in slot machines, print on demand labels for shipping and products, and for recording live rhythm strips on hospital cardiac monitors.

Through the 1990s many fax machines used thermal printing technology. Toward the beginning of the 21st century, however, thermal wax transfer, laser, andinkjet printing technology largely supplanted thermal printing technology in fax machines, allowing printing on plain paper.

The Game Boy Printer, made in 1998, was a small thermal printer used to print out certain elements from some Game Boy games.

Early formulations of the thermo-sensitive coating used in thermal paper were sensitive to incidental heat, abrasion, friction (which can cause heat, thus darkening the paper), light (which can fade printed images), and water. Later thermal coating formulations are far more stable; theoretically, thermally-printed text should remain legible at least 50 years

Hospitals commonly record fetal ultrasound scan images on thermal paper. This can cause problems if the parents wish to preserve the image by laminating it, as the heat of most laminators will darken the entire page—this can be tested for beforehand on an unimportant thermal print. An option is to make and laminate a permanent ink duplicate of the image.

@Atul Purohit