One Sunday while i was watching my grandmother's sewing machine it came on my mind to build a simple modern Sleeve for my Macbook Pro 13.3". The materials i used was what i found lying around. An old pair of blue jeans and a piece of durlap in the store room used for sack repairing. It didn't take more than one to two hours to learn how to use the sewing machine (by reading the manual and some videos on youtube) and cut the materials in the correct form.
Here is the result of the unique Candrian Sleeve
I used the bottom of the jean as a pocket in the Sleeve
As an Electronic Computer System Engineer at Delmac Instruments and in the needs of a customer i managed to develop/design a digital adjustable spirit level indicator. The main purpose was to set a zero point which means it is the starting measurement position and a limit point which will be the limit for the indication. When pitch or roll exceeds the limit point a buzzer will start ringing and indication LEDs will show the direction. There has been also added a UART interface which transfers axis values and some extra port outputs for debuging.
This is a project i designed a year ago but never built, because of not enough spare time. This month i found some free time so i started building it and i send the pcb layout for manufacturing.
All started when i received some IV-11 vfd tubes from an ebay seller i ordered from and i started testing and prototyping by first trying to simple light up the VFD tube.
A VFD tube works like a 7-segment led display with some small differences.
A) The Filaments. The Filaments exists to power the tube. We have to supply these two pins with 1.2Volt and nothing more (polarity doesn't matter).
B) The Grid. The Grid is like the common anode of a 7-Segment LED display. So the Grid has to be pushed high at 60Volt (in these tubes) in order the segments to be able to light up.
C) The Segments. The Segments light's up simple by pushing them high at 60Volt.
Here are the very first steps of powering the tube manually.
To make the powering of the tube digitaly in order to use it in the final design we have to built a simple circuit which will impliment the above description. The circuit has to be able to push each segment at 60Volt or Pull it to Ground at 0Volt. To do this two transistors (Push-Pull) are needed for each segment. One for pushing the voltage and one for pulling it down.
Push Pull Transistor connection:
We have 9 lines at each tube which need push pull transistors including Dot segment and Grid. So we have 2 transistors x 9 lines= 18 transistors in total for one tube, 28 for 6 tubes (8 lines for segments are in common for all tubes, only Grid is seperate and used for multiplexing). The number of transistors needed are enough for a fault on soldering or pcb etching (more routes) decreasing the finall product reliability and increasing cost because of the more pcb space needed. Less components more reliability.
To make VFDtube driving easier and more reliable Maxim has built MAX6921. MAX6921 is a Push Pull shift register where each bit of the register is ported on a specific pin of the device. So if we shift a bit of '1' the corresponding pin will be pushed high and if we shift '0' the corresponding pin will be pulled low. The communication to the shift register is implimented via SPI which makes it more easier as most of the MCU's nowadays have embedded SPI. By using this chip we only need 3 pins from the main MCU to impliment the SPI communication and nothing more.
Prototyping the basic powering circuit using MAX6921 VFD tube driver.
To make all the 6 display tubes used in clock, appear at the same time we have to multiplex them. To do it so we have to turn on and off each tube in the row, enough times in a second in order, the transaction not to be visible in human eye (about 70~100Hz). As you can see on the above right video multiplexing for two tubes is tested.
Testing Filaments in series.
Describing the final circuit.
The integrated circuits i have used are:
The main brain and RTC, ATMEL'sAVRAtmega168p which has SPI, 16K of memory to write plenty of code, Counter/Timer with asychronous external crystalinterrupt to update the RTC even in sleep mode, ADC for ambient light sense, an Analog Comperator for voltage drop sense to turn mcu in sleepmode when runing on backup battery and PWM to control LED brightness and voltage booster for Segments brightness.
The MAX6921 VFD-tube Push-Pull driver used for the tubes driving.
The external supply voltage of the circuit is designed to be 1A12Volt Power Plug Adapter.
To power the two chips a simple 5V stabilized power supply with LM7805 is used. Also has been used a full bridge rectifier in order to make the circuit work in any voltage polarity. At the output a low voltage drop 1N5817 diode is used to prevent back voltages.
To convert supply voltage from 12Volt to 60Volt for Grid and Segment supply a boost converted has been used which is controlled with PWM from Atmega168. The boost converter is inspired from adafruit's ice tube clock. A pull down resistor has been used at the MOSFETGate to pull it down in no operation and a 60Volt zenerdiode is added in parallel to output to prevent over voltages.
A backup battery is used to keep runing the mcu when power supply is unplagged. A low voltage drop diode 1N5817 is connected in series to prevent battery charging.
Three buttons are used for user interface (configure time/date/alarm and change menu) with pull up resistors and decoupling capacitors for spikes, AVR In System Programmer, and a voltage divider used for voltage drop sense. A decoupling capacitor is also used here to prevent spikes.
Ambient light sensor (a voltage divider with a photoresistor), a UART pinout for additional modules to be add in future and a transistor in series with a 2Wattresistor, is used to adjust filament voltage/current using PWM. Because the circuit is designed to be powered by a power plug adapter the filaments are connected in series to reduce current darw and they are supplied directly from +12V.
There have been also used 6 RGBleds, one under each tube, filling in the tubes with more color and making it more impressive. The color change depending on the selected menu.
Green: Time
Blue : Date
Red : Alarm
They are also supplied directly from the power plug adapter in order not to overload LM7805 and increase it's temp.
The main circuit.
The tube segments are connected in parallel via the bus to MAX6921 and a FET is used to turn on/off the chip. Atmega168 is connected with ISP to MAX6921. A 32,768KHz crystal is used to count the time. Also a buzzer has been used for alarm mode and button press feedback.
Crystals with frequiency 32,768KHz is used in RTC's beacuse they make perfect division with 128. 32 768 / 128 = 256. So we use this crystal with a clock prescaler of 128 and we have a counter (max value of counter 256) overflow interrupt occured once a second with accuracy of 0.002% depending on crystal.
After some modifications on my UV exposure box (scanner) for better UV expose, i desided that a better pcb must me designed for switch timer. The old one had over drilled holes and it was designed and built on my very fist steps. Also the high voltage side from the low voltage wasn't seperated as it needed to be safe.
So i redesigned it in a more compact and easier to use pcb. The firmware has been also updated and now you can program the timmer by using the two buttons. The time is calculated by timer interrupt triggering using a 32.768KHz RTC Crystal with better accuracy. The display update also has been changed from static to dynamic.
The board is homeprinted at my exposure box.
Here is the schematic in pieces.
For 5V supply used for AVR, 7-segments etc, has been used a full bridge rectifier, a big decoupling capacitor and LM7805 :
The two seven segments are connected in parallel and are updated using mutliplexing. Current protection resistors are used for each segment. Q2 & Q3 are switching each display.
Here is the relay drived by Q1 witch switches on/off the relay. On the one side of the relay is connected the AC Mains and on the other the lamps.
The AVR ATmega8. A buzzer has been used to indicate when timer is on/off and when a button is pressed. Here you can also see the RTC crystal 32.768 used to trigger the timing counter.
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 usuall 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).
The main behavour of the head is like a shift register. You shift data to be print on the head register and then you supply voltage to the elements, mapping the shifted data, on the paper. For example if you shift a value like 000011100111000111 and you power the elements you will have the '1' bits appeared on the paper with dots.
Here is a diagram showing how the data are shifted.
To print a single character you have to draw it line by line. To do this fast and simple the character pattern has to be saved on a table with all the other characters. Then you select each line of each character you want to print and you shift it on the printer register by the order you want.
For example a simple character pattern of A in 8-bit width and 9-bit height could be:
ThermometerV2.0 is coming to replace in hardware and software V1.0.
Introduction
I designed this version in the need of a thermometer for my room, built in a small pack and easy to control. The hardware is designed on a way so that the pcb can be wall mounted. At the top side of the device the PCB extents giving space for two keyhole type holes which are able to keep the device mounted on the wall. The LCD display plugs at the front side of the PCB, covering all the electronic components and giving a compact design view. The user can interact with the device using the left side switch button. The design includes a 6-pin header which gives connectivity for UART (RX,TX,GND) and for the external sensor DHT-11 (VCC,GND,DATA). Also there is an ISP-6 pin header which gives the option of on board programming. Finally there is an optional Bluetooth plug on the back side connected with AVRs UART for possible communication to other devices like mobile phones, home automation devices, pc's or whatever you imagine.
The code is written in C and is well performed in a readable way so anybody can read and modify it. For the LCD driving i have used Peter Fleury's library.
Function Modes
Display modes:
1)Celsius
2)Fahrenheit
Backlight modes:
1)Fast mode (press the button, light on, 2 seconds delay, light off)
2)Light switched off
3)Light switched on
Hardware description:
The power supply
The power supply is a basic LM7805 power supply using two pair's of decoupling capacitors before and after the regulator. Additionaly can be used the AMS1117 regulator at 3.3V. This regulator is included in the design to give the option of using a Bluetooth module which usually work at 3.3V.
The LCD HD44780 16×2 Char
A 16×2 character LCD display is used to display data to user. The only thing that somebody may not understand here is the use of BC547. BC547 is used as a switch to switch on/off LCD's back light or to pulse it using PWM adjusting the back light lightness and giving nice fading options. R3 is used to limit the current flow to transistors base, and R1 is there to pull down base voltage.
Main Brain Atmega8
The main brain of this device is Atmega8.
Note. A 16Mhz crystal has been used instead of 8Mhz shown on the schematic in order to read DHT data easier.
Peripherals
Above are the peripherals used. From left to right,
The Bluetooth module, this module is optional. It is connected to avr's uart so everything in UART can be sent via Bluetooth. For example it can send the sensor reading on a pc, a mobile phone, e web server.
TheDHT-11 sensor is used for outside humidity and temperature measurement. It has a 5k pull up resistor to Data pin to pull data bus to VCC and a 100nF decoupling capacitor to filter noise
Including an ISP header on the design makes it easy to update the software and debug on board.
For inside temperature sensing has been used the LM35.
A button is used to interact with the user. This button is pulled up with avr's internal pull up resistor and is connected to INT0 interrupt pin.
Also there is a UART pin header for optional module installation or for serial connection to PC.
More photos:
The PCB Board:
From Design to reality
The back side of the PCB and all the parts nedded for this project.
While testing the Hardware and the Software on breadboard proto.
DHT-11 is a temperature & humidity sensor in one package. It utilizes exclusive digital-signal-collecting-technique and humidity sensing technology, assuring its reliability and stability. Its sensing elements is connected with 8-bit single-chip computer. Every sensor of this model is temperature compensated and calibrated in accurate calibration chamber and the calibration-coefficient is saved in type of program in OTP memory, when the sensor is detecting, it will cite coefficient from memory. Small size & low consumption & long transmission distance(20m) enable DHT-11 to be suited in all kinds of harsh application occasions.
Characteristics:
Low Cost
Supply voltage 3 to 5V
Max current 2.5mA (while requesting data)
20-80% humidity range with 5% accuracy
0-50C temperature range with +-2C
Inside the package looks like this:
The interesting thing in this module is the protocol that uses to transfer data. All the sensor readings are sent using a single wire bus which reduces the cost and extends the distance.
In order to send data over a bus you have to describe the way the data will be transferred, so that transmitter and receiver can understand what says each other. This is what a protocol does. It describes the way the data are transmitted.
On DHT-11 the 1-wire data bus is pulled up with a resistor to VCC. So if nothing is occurred the voltage on the bus is equal to VCC.
Request:
To make the DHT-11 to send you the sensor readings you have to send it a request. The request is, to pull down the bus for more than 18ms in order to give DHT time to understand it and then pull it up for 40uS.
Response:
What comes after the request is the DHT-11 response. This is an automatic reply from DHT which indicates that DHT received your request. The response is ~54uS low and 80uS high.
Data:
What will come after the response is the sensor data. The data will be packed in a packet of 5 segments of 8-bits each. Totally 5×8 =40bits.
First two segments are Humidity read, integral & decimal. Following two are Temperature read in Celsius, integral & decimal and the last segment is the Check Sum which is the sum of the 4 first segments. If Check Sum's value isn't the same as the sum of the first 4 segments that means that data received isn't correct.
How to Identify Bits:
Each bit sent is a follow of ~54uS Low in the bus and ~24uS to 70uS High depending on the value of the bit.
Bit '0' : ~54uS Low and ~24uS High
Bit '1' : ~54uS Low and ~70uS High
End Of Frame:
At the end of packet DHT sends a ~54uS Low level, pulls the bus to High and goes to sleep mode.
Logic Analyzer Snapshots
In the following image you can see the request sent from the MCU to the DHT and following the packet. Because the request has very long duration as you can see is about 20mS and packet received is in uS we can't view the data bits.
If we zoom at the data bits we can read the values. You can see after the Request follows the Response, and Data bits. I have drawn some color notes to be more understandable.
If we decode the above data we have.
Humidity 0b00101011.0b00000000 = 43.0%
Temperature 0b00010111 = 23 C.
The last two segments can't be seen in this image because of zoom.
Implementation:
What we have to do to read a DHT-11 sensor is:
Send request
Read response
Read each data segment and save it to a buffer
Sum the segments and check if the result is the same as CheckSum
If the CheckSum is correct, the values are correct so we can use them. If CheckSum is wrong we discard the packet.
To read the data bits can use a counter and start count uSeconds of High level. For counts > 24uS we replace with bit '1'. For counts <=24 we replace with bit'0'
Here you can find some code to read DHT-11 using an Atmega8 at 16Mhz
In the need of controlling a 7A20Volt DC Motor i designed a speed controller with some cheap components. The circuit is a digital circuit and works with Pulse Width Modulation (PWM) which is one of the best ways to control a dc motor. This circuit can drive up to 33A10V DC motor with a big heat sink placed on the switching mosfet.
Summarily i used in this circuit, the AVR ATtiny13 to control the PWM , a n-mosfet IRF540N for switching the motor and a Rotary Encoder to adjust the PWM Duty Cycle.
Note. The same circuit can be used as a light dimmer for LEDs.
The circuit consists of:
The Power Supply.
It is a basic LM7805 power supply which adjusts the voltage at 5V for powering the ATtiny13 and the LEDs. Capacitors before the LM7805C10, C7 and after C8, C11 have been used for noise filtering. Diode D11N4001 is there to protect the circuit from inverting voltages.
The main circuit.
The main circuit can be separated in 4 sub circuits to be more understandable.
The LEDs
3 Leds have been used for indicating PWM Duty Cycle value: Minimum (LED3), Maximum(LED2) and the Current Value (LED1). LED2 and LED3 are connected directly to the ATtiny13 I/O. LED1 which indicates the current PWM Duty Cycle value is driven by the transistor T1BC337 triggered by the PWM output. R1 R3 and R4 are current limiting resistors for LEDs. R2 Limits the current draw to the BC337 base.
The Rotary Encoder
This is the Rotary Encoder connected with the appropriate components to work properly. R6 and R5 are pull up resistors which "pulls" A and B pins to VCC. Pin C is directly connected to GND. C4 and C3 are decoupling capacitors which are appropriate for noise filtering. If you don't place them the noise will be not filtered and the rotary probably will not work.
The Motor Switcher
For Motor Switching i have used a n-mosfet IRF540N which can Continuous Drain Current, VGS @ 10V 23-33A depending on the temperature (25C-100C). Diode D2 has been placed for inductor inverting voltages. Capacitor C1 is there to filter the noise provided from the motor. If you don't place this capacitor you may have noise at the rotary encoder and it will not work properly.
Make sure you have placed a heat sink on the IRF540N because at high currents it is getting realy hot!
Here you can find photos of the test circuit i built.
