Archive for the 'Instructable' Category

Step Pulse Extender – PSoC Style

The TB6600 stepper drivers I have in the X-Controller have a “Torque” feature.  You set the motor current with a reference voltage and the torque feature allows you to easily switch between that current and 1/3 third of it. This is typically used for an idle current reduction feature at the system level.

tq_schm

Why Idle Reduction?

Stepper motors have a lot of hold torque, but that torque quickly falls off with speed.   Therefore you typically size a stepper motor and set the current for your maximum cut or rapid speed.  This means your motors will have excess torque when idle and will tend to run hottest at idle.  You basically the the current as high as possible until the motors get too hot.  If you could reduce the current at idle, you would reduce the temperature and could set the current higher than normal when spinning.

This is great, but the machine will never be in idle during a long job.  At least one of the motors should always be running. If you could figure out when each individual motor was idle, you handle each motor independently.  That is not easy in firmware, but there are tricks to do it in hardware.  You could tie the feature to the step pulse.  Whenever the step pulse is active, the full torque could be active.  That has two problems. The step pulse is extremely short, in the range of a few microseconds.  The other is you might want the current high for a a short bit after the motor goes idle just to make sure the machine is stable in the new position.

The trick is to use the step pulse, but extend it to the desired duration.  It should stay on through all the step pulses and extend the last pulse.

Discrete Hardware Solution

The X-Controller uses a discrete logic chip to do this. It uses a retriggerable monostable vibrator (74HC123D).  The R/C circuit on the right of the schematic snippet sets the duration. It works great, but this adds a lot of parts and things are locked down and not easily adjustable. If you needed to override this function, you have to break out the soldering iron.

PSoC Solution

With PSoC, when you hear “discrete logic” you should know there is probably a good way to do it on the chip. In this case I designed a custom component using verilog.

The verilog code is quite simple.  The best part is none of this is done on the CPU, so there is no impact on the motion control performance. What the video to see the details.

 

Full color 3-D viewing Stand For iPad

iPad 3D Viewer

Thomas Kumlehn of Pixel Partner sent me a nice email regarding the iPad Chair.  He did a roughly similar Instructable to mine on an iPad 3-D viewer.  This is another laser cut flat-pack iPad holder, but this holds the iPad in the perfect location for viewing stereoscopic 3D images and video.  He uses a readily available lens the redirects your vision to over under pairs.  The iPads portrait mode works very well for this.

I remember as a child, a friend had a vintage side by side stereo viewer with a bunch of black and white pictures for it.  I remember how amazed I was by them.

He has files available for cutting on his web site.

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Laser Wood Burning Pen

There is an Interesting Instructable on integrating a 1W fiber coupled laser into a pen.  The whole project is a rather low tech approach, so it shows how easy it is to do.  I found a few of the fiber optic coupled laser diodes on eBay, all for less than $100.  In the video, it does not appear to burn real fast, but it still looks usable.