Haris Andrianakis writes:
One of my latest projects i just finished is a hardware thermal printer driver. This project designed/developed for “Delmac Instruments” as a part of my internship. Thermal printers are used in cash and weighting machines for receipt printing.
What the specific hardware does is to receive ASCII characters, escape sequences in UART and convert them in a printable form to send to printer mechanism for printing. Escape sequences are used to send commands to the printer to change character size, line spacing etc.
Thermal Printers don’t use ink as usual printers but they have a head of tiny resistors in a row (about 384) which behave on the paper as dots. Also they use a suitable paper which is thermal sensitive.
By supplying voltage to a single resistor, you heat the resistor and you make the paper burn at the specific point drawing a tiny single dot on the paper. If you supply voltage to a single resistor and you move the paper at the same time by stepping the head motor you will have a tiny width vertical row. This is the basic. (Resistors are refered as elements).
Thermal Printer Driver – [Link]
Boris Ribov, Georgi Bakalski writes:
If you have a website, blog or any other web service then the etherfeed is for you. The etherfeed is a small standalone network device, it connects to the Internet and displays statistical data about your website like number of unique visitors, number of pageviews, PayPal sales (SUM of sales via the PayPal IPN), Facebook likes for your brand / group and weather data like temperature, humidity for your location.
How it works?
The system consist of two parts. The first part is a set of php scripts responsible for collecting data from Google Analytics, PayPal, Facebook and Google weather data. These scripts shall be installed on the target website.
The second part is the etherfeed device which connects to the internet via a router, and access one of the above mentioned php scripts, collects the data and displays it on the etherfeed 16×1 Blue backlight LCD Display.
Etherfeed – tickling your ego or statistics? – [Link]
Kerry uses a DIY serial display to show debugging data sent from an Arduino’s UART. Sometimes the data comes too fast to read, so he added a 4K buffer and controls to scroll thorough the history. [via]
…if your application generates a lot of messages, it would still be hard to spot the relevant information as you can only see the last couple of lines of the data.
So my solution is to add a none-volatile off-screen buffer to the serial display so that multiple rows of data can be captured during run time and retained for later debugging.
Serial port monitor with 2×20 LCD and 4K text buffer – [Link]
Charalampos Andrianakis writes:
The idea of explaining here how a rotary encoder works began from the need to use a rotary encoder myself for adjusting a PWM which drives a DC motor. So i started looking for how a rotary works. When i understood how it works i thought that it could be a good idea to show you and explain what i learned.
Anyone who has worked on circuits before has used an analog potentiometer. If you are new in electronics here is a quick explanation of what a potentiometer is. In a few words a potentiometer is a varying resistor which value changes by turning the knob. By the Ohm Law V=I*R implies that it can be used for voltage or current adjustments. An example of potentiometers use is in front panels for varying values e.g in a work bench power supply to adjust the voltage or the current.
Well the potentiometers have some disadvantage.
- Produce noise at knob turn over the uses or if dust has passed in.
- They are not that accurate.
- To use them in a digital circuit you have to use an Analog To Digital converter.
On the other hand Rotary Encoder.
- There is no noise production (if you use the appropriate capacitors).
- They are accurate (they have steps).
- There is no need of a digital to analog converter.
3-pin Rotary Encoder How to – [Link]
Displaying content on a normal alphanumeric display is very limited ,we have to be limited with the font size and we can’t draw any graphics also. but convention Graphics lcd are really very expensive so here is the solution, you can use Nokia 3315 monochrome LCD to display your large font text and graphics . the reason behind using this LCD is ,it is really very cheap and can be powered with 3 volts supply. so it is really good for battery powered application.
Nokia 3315 LCD interfacing with Microcontroller – [Link]
This morning I decided its about time I learn how to use the UART hardware in most PIC microcontrollers. I started off with a USB-RS-232 converter that I got for US$3 from DealExtreme. There are a few reasons why I used a converter, firstly being because my main PC no longer has an RS-232 port since its old tech, but also because I thought it’d be alot neater for my projects to have a USB connection and it means I can interface with TTL signal levels (0-5v) instead of the RS-232 standards -12v – +12v which would have added complications, but we’ll get back to that just now…
Learning Serial Communication – [Link]
Touch screen or touch activated technology has been around for a few decades now, but only recently have prices dropped and the technology been (somewhat) perfected. As an input device touch screens offer a more natural interaction that humans are used to, which offers a great advantage for businesses selling to the general public over traditional keyboards and mouses.
This article will look at how to interface to a 4-wire resistive touch screen and find out the X and Y coordinates of the current point being touched. A minimal number of parts will be used to simplify the system hardware, and to focus more on the theory of how it works.
Simple Touch Screen Interface – [Link]
A friend of mine suggested that I build something for a 74xx TTL discrete logic contest at dangerous prototypes, so I figured why not? If you like this design, make sure to leave a comment on their website for my competition entry.
The Masochist’s video card is a pure TTL discrete logic design that generates the necessary video signals for VGA. The project name came about after the hours I spent wire-wrapping the project together yielded painfully raw fingertips. So be fore-warned if you duplicate this project, don’t abuse the wire-wrap tool!
Masochist’s Video Card – [Link]
The keyboard is the most common way for humans to input information into a computer. It has been around since before computers were main-stream and everyone was still using typewriters. Because of this prevalence in society, it’s important that we understand how to interface to the basic PS/2 keyboard.
This article will describe and show you an example of how to create a system capable of interacting with a keyboard in order to understand what keys have been pressed. The example system will be built on a breadboard using a PIC microcontroller to communicate with the keyboard and display output.
PS/2 Keyboard Interface – [Link]
VT220 serial console (circa 1983) set up as a terminal for Mac Pro (2010) – [via]
My biggest source of information getting this going was Paul Weinstein’s post about setting up an Apple IIc as a terminal for his Mac mini (which is similar, but not quite the same since the IIc still has to emulate the terminal in software). I got the same USB-to-serial adapter, a Keyspan USA-19HS ($27), which has Mac drivers that I can happily confirm work well with 10.7 Lion. I also needed a null modem cable ($7) and 25-pin female/female converter ($4) to connect it to my VT220.
At first I used the same method as Paul to get it working, gluing together the terminal and OS with a utility called screen. As Paul notes, this is less than desirable. It still requires you to open a software terminal to make the connection, and you’re still operating through a layer of emulation. On most Unixes you can simply add a line to /etc/ttys and everything just works via getty, but apparently this has been disabled in OS X since 10.5.
Eventually I found this page, which explains the problem and how to fix it. After adding a line in /etc/gettytab to manually set the terminal type to vt220-8bit everything works perfectly! A real hardware terminal directly connected the old fashioned way, with no emulation. Awesome
VT220 serial console (circa 1983) set up as a terminal for Mac Pro (2010) – [Link]