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General information

This is a simple script that is intended to be used with the tinkerforge stepper brick and the IO4 bricklet.

Purpose of the setup is to let a stepper motor advance a certain amount of steps everytime a TTL pulse is registered at pin 0 of the IO4 bricklet. In addition to that the current position is registered as No. of steps and angle (using a specified gear ratio) that way one can set and return to a "home" position.

This (and some mechanical parts) form an automatic goinometer for an EPR- spectrometer.

Usage

Be sure to have installed and started brickd as described below. Connect the brick/bricklet to a free USB port of the computer and start the programm by running:

./goniometer [OPTIONS]

It will then listen for interrupts on the IO4 bricklets or key presses on the computer. Available options are:

-a,  --angle       Angle by wich motor advances on interrupt (default: 5)
-g,  --gear-ratio  Gear ratio between motor and sample rod (default: 2)
-s,  --steps-per-revolution Number of full-width steps needed for one revolution of the motor rod (default:200)
-m,  --step-mode   Perform 1/n steps. Note 1/1 steps give the biggest torque. (n = (1,2,4,8); default: 1)
-d,  --dynamic     Dynamic mode: --angle is ignored and instead TTL pulse length is used. 10ms = 0.1deg
-r,  --no-record   Do not keep a logfile that records every angle
-t,  --trigger     Trigger spectrometer instead of being triggered by it (for CW measurements)
-w,  --sweep-time  Time spectrometer needs for field sweep and to ready for the next one (with -t)
-n,  --n-aquisitions  Number of field sweeps/aquisitions (with -t)

For now the Brick/Bricklet UID needs to be specified in the C-code and thus you need to recompile it for every new step.

Usage example

Imagine the motor has a gear with 50 teeth fitted to its rod. This gear meshes with a gear with 100 teeth at the sample rod of the spectrometer. For this configuration the gear ratio is 2. The motor has to turn twice to make the sample rod turn once thus increasing the delivered torque as well as the precision.

You use a motor with 200 steps per revolution (1.8° per step) and want to operate with 1/8 steps which will cause the least vibration but will also deliver only a small torque.

The motor shall advance by 5° after every TTL pulse. Note: This will not be possible with the 200 steps per revolution motor. Instead you will get a 4.95deg step (with 1/8 steps) and 5.4 (with full steps). A better choice would be e.g. a 9deg step size.

Connect the stepper per USB and to the spectrometer and run

goniometer -g 2 -s 200 -a 5 -m 8

The length of the TTL pulse does not play a role in the above example. If you want to specify the angle to advance after the TTL pulse use

goniometer -g 2 -s 200 -m 8 -d

This activates the "dynamic mode" where the angle to advance by is given by (pulse length[ms])/100 [°]. So for again a 5 deg step the pulse needs to be 500ms long.

Compilation and Prerequisites

The programm depends only on pthread on POSIX systems and Winsock2 on Windows systems. Use of MinGW for compilation on windows is recommended and the provided makefile will work for this environment and unix like systems (including Mac OS/X) as long as gcc is installed. So executing

make

will compile and link the code and place the binary in the bin/ directory. Precompiled binarys that work on Windows 7 Professional (64bit) can be found in bin/.

For manual compilation see the excellent tinkerforge API documentation.

The programm connects to the brick deamon. Its available for most common operating systems. It needs to be downloaded and installed from the tinkerforge website's download section. It will then run run as a daemon in the background.

Getting started with MinGW

The unexperienced MinGW user might find the following steps to set up and use MinGW on Windows helpful:

  • Download the newest installer for MinGW
  • Execute the downloaded setup. Click yes, "I agree" and next until...
  • ... you can choose the components. Choose at least the C/C++ compiler and MSYS Basic System. Finish the installer.
  • Launch the MinGW shell (You should find a shortcut in the start menu.)
  • Go to the folder where you downloaded the sourcecode to. Do this by typing cd /C/User/.../goniometer. Note that a normal slash ( ´/´ ) instead of a backslash ( ´\´ ) is used and that the drive C is denoted by ´/C/´ instead of ´C:\´. Hint: Hit TAB to autocomplete the folder.
  • Type make this will compile the code and put the binary in ./bin/
  • If you whish, you can execute the program right away from the commandline by typing ´bin/goniometer.exe`

Link to docs

Further documentation can be found in the doc/ directory.