Member Since: April 21, 2008

Country: United States


Programming Languages

Spin and PASM for the Parallax Propeller chip. Some C for PC and AVR microcontrollers.


Robots, data logging, wireless networks



  • I think part of this tutorial is confusing (and wrong). I think the statement “it’s also possible to load down a circuit too little - this may let too much current flow” is contradictory. If a lot of current is flowing the load will be high. I think the tutorial is using the term “load” incorrectly in this case. I assume the author meant it’s possible to not add enough resistance which would cause too much current to flow. Too little resistance would cause the load to be too large not too small. There are power supplies (i.e. PC power supplies) which require a minimum load to work properly but power supplies which require a minimum load are the exception. As the author confirms elsewhere in the tutorial, in general one can not have too small of a load on a power supply. I think it would be a good idea to change the wording in this tutorial so the term “load” is used in a way consistent with its definition in this application.

  • Sorry for such a late reply, but I’ve used HobbyKing HXT900 servos in several projects and they seem to be very strong for their size.

  • 4 AA cells probably do not provide enough current for the 12 servos. You can find more information at this post on Let’s Make Robots. According to above post, you need a minimum of 7V. You probably need a battery pack which can supply 3A or more. Many rechargeable batteries can source more current than alkaline cells. Edit: I should have read more carefully. I see you have the robot up and running. Very good.

  • I think the description should be clarified to make it clear there are (usually) four transitions per “click” of the encoder. You’re right about the 96 transitions per rotation.

  • These are fun encoders. IMO, you should clarify the description to say the “24 Pulses per Rotation” means 24 full encoder cycles. Each “click” of the detent will transition the encoder through a full cycle of four transitions. There are 96 transitions per rotation (as Mayo2017 mentioned earlier).

    Since there are four transitions per detent click, pressing the button can cause the encoder to fluctuate a couple of transitions.

  • I’ve always been able to get them back off. I’m sure I’ve removed four different knobs from encoders dozens of times. I have had to pull pretty hard a few times.

  • Thanks for the link. I was pleased to see the slot for a ribbon cable. I’m pretty sure I’ll get one now (or when they’re back in stock).

  • You’re right. I just checked the list of commands and there is a “status” command. The printer will let the program know if there is page or not (and some other info) when asked.

    Very cool. Thanks.

  • I think a 24V 280W scooter motor is probably beyond what the T'Rex was designed to power. I’d think you’d be better off with a controller designed for scooter motors.

  • SparkFun’s ProtoBoard works well with the Propeller chip. You’ll want to use 0.1uF caps close to each of the four Vdd pins. Unfortunately SparkFun’s Propeller bob doesn’t have these bypass caps. The Propeller’s PLL circuit is very sensitive to current running through them. The Vdd pins all need to be powered at the same voltage to prevent damage. The best way to keep all the Vdd pins at the same voltage is to provide each pin with its own bypass cap.

    I’m a big fan of the Propeller myself. It makes a great controller chip for robotic projects.

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