佳能EF镜头SPI控制|天天快讯

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使用廉价的MCU，搭配SPI协议驱动你的佳能摄像头。逆向Canon EF卡口镜头，这个是昨天的文章。ASCOM EF Lens Controller – control unit for Canon EF/EF-S lenses. It allows you to control lens using the ASCOM platform tools.Features (supported by driver):focus control;aperture value control;temperature measure (additional sensor required, e.g. popularDS18B20).This device uses SPI interface. Description of lens commands were taken from published articles about reverse engineered internal Canon protocol.Connection to lens is easy. It is only necessary to know pinout of itscontacts. This information is available on the Web. Just «google» canon efpinout. I recommend to use a scheme, shown below.This picture describes electric pins on lens or special macro-adapter which issuitable for soldering wires. You can buy adapters in any photo shop or onweb stores such as EBay. It looks something like this.Next component – microcontroller, which support SPI interface. It may beATmega, STM32, PIC or board, based on its controllers. Factory PCB has allrequired components and will be easy for beginners while simplemicrocontroller allows you to make own custom device.I used Arduino Nano based on ATmega328P controller. Its performance isenough for our purpose. Small size and low cost - its advantage.Pinout diagram above shows the designations of Arduino Nano contacts. Sowe need:Note: only huge lenses may require external power supply. I tested mylenses (EF-S 18-55, EF 50/1.8, EF200/2.8L) and measured their currentconsumption. It was less than 200 mA. It means that these lenses can bepowered directly from 5V Arduino pin. Entire system will be powered fromUSB, and there is no need for additional wires.You can experiment on the breadboard but for the final design it is better touse a more respectable solution.I want to point out one feature associated with Arduino. Now, these boardsuse the Automatic (Software) Reset, which is convenient for firmware uploadbut do not really need us. The fact is that:One of the hardware flow control lines (DTR) of the FT232RL is connected to thereset line of the ATmega168 or ATmega328 via a 100 nanofarad capacitor. Whenthis line is asserted (taken low), the reset line drops long enough to reset the chip.This means that each connection («Connect» button in MaximDL orFocusMax) to the device will cause it to reboot. Result is 3-5 sec delay. Ifyou are not satisfied, simplest solution is to unsolder DTR pin to preventtransfer of reboot signal. I used «ChinaDuino», it has CH340G as UART chip.Original Arduino uses FT232RL.These schemes allow you to easily find the DTR pin. After making thesechanges, device connects immediately.SoftwareSoftware consists of two main parts:Arduino sketch (firmware) is responsible for interaction with lens;ASCOM device driver.Unit relations shown in the figure below:The red highlighted functionality implemented in addition to the mainfunctions realized in driver pattern. Focuser driver has no iris controlfunctions by default. But aperture value control is important feature.代码使用我就不写了，后面我会上代码：Use P# to get current focus position (5000 by default)Use Mxxxx# to move focus, e.g. M5270#Use Axx# to change aperture value, where xx – count of steps (1/3EV). 0 – wide open on your lens.

下载这个控制软件，有一种年老失修的美

ASCOM

Click «Properties», you can see driver setup dialog. Set requiredparameters:

COM Port Number – controller connection port;

Lens Model – choose your lens from drop-down list. In fact youcan use any lens. Just add it to lens.txt which is in driverinstallation folder and insert all aperture values of lens;

Aperture Value – select required aperture value. Changes will besaved in EEPROM of Arduino chip.

After all changes are saved, you can connect to the controller.Temperature will be displayed only if you connect a sensor. I usedanalog KTS-1 sensor. GET TEMPERATURE section in my sketch work with this sensor. You can use any other. Do not forget to correct your sketch. If you do not need to measure temperature just comment this strings.