There are some digital levels on the market that are really nice tools to have for a variety of purposes. I grabbed a DXL360 and am really happy with it so far. When I wanted to do an angle vs. time calibration measurement of my Barn Door Startracker over 10s of minutes, I really wanted to get the data from the level into a computer so I could plot and process it a bit.
The level has a USB port but the manual suggests that an optional attachment is required to get it into a computer, at least for this model. However, the manual also states that data comes out of it in RS232 format. I bet I could read that data with some more generic equipment that I have sitting around. And it turned out to be easy. This post shows how I did it.
First, I cut a USB cable in half to tap into the level. As a check, I hooked the data lines up to my oscilloscope. I was greeted with a binary bitstream that changed pleasantly as I rotated the level. Looks promising.
Next, I just plugged the data cables into my extraordinarily useful Adafruit FT232H breakout board, which is basically a universal attachment for these kinds of things. I love this chip. In this case I just plugged the TX line (white in my cable) to the UART RX line on the chip (D1) and GND to GND.
To test it, I just followed Adafruit’s instructions to open up a screen session on my (linux) laptop. I was immediately greeted with and ASCII stream of data in a meaningful format. The FT232H starts up in its UART serial mode by default which is exactly what I needed for this device. Yay: this is an easy project.
Since I didn’t need any advanced features of this chip for this project, I didn’t need to use the Adafruit library or anything. I just wrote a bit of Python 3 code to parse the data:
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""" Digital Level Reader. Reads DXL360 digital level measurements coming in over the serial port. Data comes in via UART, converted to USB with a FT232H or equiv. Format is X+0000Y+0000 Original Purpose: Calibrate/verify star-tracking barn-door camera mount. By: Nick Touran """ import serial import re import time DEV = '/dev/ttyUSB0' BAUD = 9600 MSG_LENGTH = 12 def read(): with serial.Serial(DEV, BAUD, timeout=1) as port: # sync up when you find an 'X' character char = b'' while char != b'X': char = port.read() port.read(MSG_LENGTH - 1) # toss one datum since X was consumed start = time.time() seconds = 0.0 # now read continuously and process into floats while True: datum = port.read(MSG_LENGTH).decode() match = re.search('X([+-]\d\d\d\d)Y([+-]\d\d\d\d)', datum) if not match: raise ValueError('Level did not provide valid data. Check connection.') x, y = match.groups() x = int(x) * 0.01 y = int(y) * 0.01 seconds = time.time() - start print('{:<10.1f} {: 6.2f} {: 6.2f}'.format(seconds, x, y)) yield (seconds, x, y) if __name__ == '__main__': read() |
This code creates a generator that you iterate over very simply for whatever application you need. For my calibration stuff, the plotting code looks like this:
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import matplotlib.pyplot as plt import level def measure(duration_in_seconds=20): t, x, y = [], [], [] for seconds, xi, yi in level.read(): t.append(seconds) x.append(xi) y.append(yi) if seconds > duration_in_seconds: break plt.plot(t, x, '.') plt.xlabel('Time (s)') plt.ylabel('Angle (degrees)') plt.title('Level data') plt.grid(alpha=0.3) plt.show() |
That just reads some data and then plots it, like this:
Sweeeeeet.
Coupling a computer to this level really makes it an even more awesome and useful instrument.
Update: I open-sourced this software as part of the startracker project on github.
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