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Altimeter and telemetry module with video On Screen Display |
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Description ALTI-OSD module is a miniature instrumentation system designed to display data on a video monitor. Its On Screen Display feature is PAL and NTSC compatible. ALTI-OSD basic functions are : high precision altimeter with temperature compensation, 3 inputs voltmeter, and event counter. As options, external sensors can be connected to ALTI-OSD to display temperature, compass bearing and wind speed. All information and data necessary to build, install and operate the ALTI-OSD module is available in this page. |
 ALTI-OSD module |
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Main features |
 Picture example |
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www.gentles.ltd.uk/gentvu/altiosd.htm |
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| ALTI-OSD use instructions |
Wiring instructions Wiring of ALTI-OSD is very simple : you only have to connect the video output of the module (pin 1 and 2) in parallel with the external video signal. ALTI-OSD is powered by any DC voltage between 5.5V and 12V. Typical consumption is 35mA, which enable 5 hours of operation with a 9V 6LR61 battery. |
 The device connected to the Video Input may be : a mini video W&B or color CCD camera, a digital camera or the analog video output of a camcorder. The device connected to the Video Output may be : a video transmitter, a LCD video monitor or a video projector. * A 80 to 100 ohms load resistor is necessary if the input impedance of the device connected to the video output of the module does not present the 75 ohms normalized value. Warning : Intersema pressure sensor is light sensitive : to ensure accurate measurement, a dark cap is necessary to protect the sensor from light exposition. |
Application example Picture below shows the application of ALTI-OSD in a transmission system of the video signal produced by a digital camera CANON IXUS 400. |
 A single 9V battery supplies the ALTI-OSD module and a 2.4GHz micro transmitter. IXUS 400 video output, 2.4GHz micro transmitter input, and ALTI-OSD video output are connected together through a RCA "T" plug. The picture provided by IXUS 400 is received and displayed on a mini LCD 2.4GHz receiver and monitor, with indication of altitude and 9V battery voltage. |
Push-button operation A short push resets the altitude and the event counter. Altitude reference and counter value are saved during power off. A long push of duration more than 5s enters the configuration mode, used to modify the programmable parameters of ALTI-OSD. |
 Picture example |
Configuration mode instruction manual The flowchart of the configuration mode is shown here and is available here in PDF format. The configuration is controlled by the push-button, and enables to set 11 parameters including language, units, text position and optional data display. Modified parameters are stored in a permanent memory, and saved during power off. |
 Configuration flowchart |
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| Connection of optional extensions |
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Event counter The event counter is incremented at every connection of the CTR pin to GND. CTR pin is pulled up to +5V by a 27kohms resistor. Maximum value of the counter is 255. This counter can be used to display the number of pictures shot by a camera triggered by a remote control. Counter value is set to zero by pressing the push-button. Display of event counter is programmable through the configuration menu 7. |
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Voltage 3 voltage can be displayed : Input voltage range is 0 to 18VDC. Input impedance is 37kohms. Display of V0 voltage is programmable through the configuration menu 5. V1 and V2 voltage are automatically displayed when they exceed 50mV. |
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Temperature Pin 22 DQ is dedicated to the connection of an external temperature sensor DALLAS DS1820 or DS18B20. Temperature is displayed in °Celsius or °Fahrenheit depending on the selected unit (menu 4). Sensor reference (1820 or 18B20) is selected through menu 9. |
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Wind speed Pin 6 ANEMO is dedicated to the connection of an external rotary anemometer. ALTI-OSD calculates the product of the pin 6 frequency by the GAIN ANEMO ratio. The ratio is adjustable from 0 to 4km/h/Hz through the configuration menu 11. The frequency is measured during a time space of 1/2 second. The frequency shall be lower than 500Hz. ANEMO pin is pulled up to +5V by a 27kohms resistor. This input is a Schmitt trigger type with a low threshold of 1.5V and a high threshold of 2.75V. This input can be connected for example to a magnetic switch or to the TTL signal provided by a logic comparator. Wind speed is displayed in km/h or mph depending on the selected unit (menu 4). |
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Compass bearing Pin 17 to 20 are dedicated to the connection of the compass module CMPS03 developed by Devanted Ltd (www.robot-electronics.co.uk). CMPS03 is powered by the ALTI-OSD internal +5V. ALTI-OSD reads the bearing angle via I2C bus. Recognition of CMPS03 is automatic. Compass bearing value is displayed in degrees. |
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External push-button Pin 8 SW is dedicated to the connection of an additional external push-button having the same functions as the internal one. Such an external push-button is necessary when the ALTI-OSD is located in a non accessible location. SW pin is pulled up to +5V by a 27kohms resistor. Input threshold is 1.5V typical. Pressing the push-button corresponds to the connection of SW pin to GND. |
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Optional data display |
 SI units | 
GB units |
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ALTI-OSD pinout |
 Note : pins 1, 3, 7, 10, 15 and 17 are connected together inside the module |
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| Do-It-Yourself instructions ALTI-OSD module can be built in 2 versions : External pinout of both versions are identical. All data necessary to build the 2 versions are available in the table below. |
Critical component in ALTIOSD module is pressure sensor MS5534AP produced by INTERSEMA. MS5534 is a SMD ceramic substrate including a miniature ceramic sensor, an analog to digital converter and read only memory hosting calibration coefficients. This sensor provides a highly accurate pressure measurement in a very compact size. MS5534AP is distributed in France by SELECTRONIC. INTERSEMA datasheet advises against hand soldering of the sensor, because of the risk of overheating the device. I personnally soldered by hand 5 devices with a low power soldering iron and had no problem. A solution to avoid overheating risks is to solder thin cables on the little solder bumps located on the sensor. Other components are more widely available. See last paragraph of French Electronic workshop page to get French distributors name and address. CAD PCB files are fully compatible with Freeware version of Eagle version 4.11r2 Light, downloadable on CADSOFT web site. Some design information Characters generation, computation and general sequencing are done by a PIC16F876 microcontroller running with 20MHz clock. The PIC is synchronized with the video signal at every line synchro pulse with a 50ns precision. The width of a pixel corresponds to 2 instructions of the PIC, i.e. 400ns. To master all tasks in stringent real time constraints, PIC software is written in highly optimized assembler language. Binary code size is 13kbytes. Temperature sensor acquisition is based on the 1-Wire Dallas protocol, with "Parasite Power" mode. |
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Altitude calculation The formula used to calculate height from atmopheric pressure data is : P0 = 1013 hPa s = 1 / 5.2563 A = 2.2555E-5 The software run by the PIC uses a 2nd ordre polynomial approximation. It gives a good accuracy from 0 to 3500. This approximation requires only a 32 bits x 32 bits unsigned multiplication. H[m] =(((745 * Q) / 256 + 46597) * Q) / 65536 - 966 with Q = 11390 - P P = ambiant atmospheric pressure in tenth of hPa or mBar. |
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KESTREL impeller Anemometer sensor is a 25mm impeller produced by KESTREL. Rotation speed is measured by magnetic coupling. The signal conditionning schematic is build with a TLC 271 operational amplifier. OUT signal is directly connected to the ANEMO input of ALTI-OSD module.   Detailed data : |
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Archive Former version of video altimeter designed with Motorola MPX2100. |
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