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Showing posts from December, 2017

Building a Prusa i3 MK2S

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A friend needed a 3D printer for a project and I recommended him an MK2S as he was in a hurry. Printer took three days to get here and after the holidays we had to build it yesterday, but the flu forced me to delay that.



The good thing about doing yet another build is that I am quite familiar with the design and the kit, and the problem is that I am quite familiar with the design and the kit too. The latter makes you skip steps and/or fast forward into the build so you have to stop, go back to where I messed up, follow the instructions to the letter and get back on track.

Even funnier [so to speak] is when you know something is important no to skip (like which side should be up on the Y-carriage) and still missing the point: I knew it was important to make sure to identify the side with the mark. The picture showed the mark upward. Next picture detailed where the first linear bearing should be placed on, so just went on with the instructions, assuming the mark should be up while doing…

H-bridge and PWM for DC motor control

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Several times when controlling a DC motor with PWM over an H-bridge I asked myself what could be better during the OFF part of the PWM cycle. I reckon three basic choices are possible:

If all the switches are OFF, then the back EMF will flow through the flyback diodes of the bridge.The same action as above could be achieved if the switches opposite to the PWM-ON cycle where ON during the OFF period. A braking action is caused.The motor could be shorted by closing the top (S1+S3) or bottom switches (S2+S4) thus shorting motor current and again creating a braking action too. Options 2 and 3 correspond to the fast and slow decay modes when the H-bridge is used for controlling one coil of a stepper motor. And even there, it is possible to mix and match so both can be used during a percentage of the PWM OFF time. 
But my doubt came from a user of my dcservo project, who alerted me that a motor was burned and he thought it was caused because my code was using option 3 during the PWM OFF tim…

Helping video projectors to behave

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My friend, artist, and colleague was planning an Arts exhibit and asked me a simple question: How can I best [automatically] switch off some video projectors I am using?

After some experience, I have come to realize that Interactive Art projects have the additional complexity of day-to-day starting and stopping. Most places have staff who can take care of operating an electric switch or a remote control, but anything more complex than that and you are in trouble and the success of your project may be jeopardized by improper setup. So it is the best interest of the artist to streamline the process as much as possible.

It is really not a problem to ask the staff to switch on an Arts installation using a remote control but, if you want your piece to shut down by itself you may need some convincing. What is really a bad idea, and unfortunately I am witnessing this with all kinds of equipment on campus, is to just remove power from the device you want to switch off. The reason is that many…