Chips Getting Hot

SRLM

Question: how hot is the PSC supposed to get when powered by USB?

I think I may have fried my chip. The situation is as follows: when I hook up the USB PSC to the cable (USB) it heats up to about 160 degrees F in about 10 seconds. At first, I thought it was because I had shorted it. But no, when I removed it from the housing and dangled it by the cable: same thing. My concern is that I had shorted it before: what happens when the five contacts (3 for the switch, two for the terminal block) are electrically connected?

I tried running the software, but it doesn't seem to control a servo. I see the FTDI usb LED flash when I change a command on the PC, so I'm assuming that I get the data correctly.

Post Edited (SRLM) : 11/4/2008 5:57:08 PM GMT

Chris Savage

Sounds like perhaps servo power was introduced into the controller power system...it sounds like it was damaged and is going into thermal run-away.

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Chris Savage
Parallax Engineering

SRLM

Ah. So I'll ask: is the chip fried? I don't suppose Parallax sells one of those center chips by itself... Note: the temperature holds at 160 F. It doesn't go any higher or lower (at least in the five minutes that I measured)

Chris Savage

The chip is not available separately. However you may be able to contact our Tech Support Dept. and they may be able to help you out.

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Chris Savage
Parallax Engineering

SRLM

Okay. I'll get on that. One other question, semi related ...

On my PPDB board, I hooked up a stepper motor to the L293 chip. Input voltage is 9 V 1 A. A similar thing happened: when I ran the code from the N&V column, "Stepping out with Spin", the chip gets very hot. In about four repetitions of the program, the temperature had risen to 160F. It's very consistent, a steady rate of about 2 degrees per second. I was afraid to let it go any higher. Is it that I'm drawing too much current? I'm taking it in later today to measure and see how much I use, but if it's not that, then what?

Chris Savage

SRLM, what is connected to where (be clear in your connections) and which chip is heating up?

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Chris Savage
Parallax Engineering

SRLM

Sorry about the short info. The motor driver chip gets hot, while the prop stays ice cold. Connections are pretty much the same as in the N&V article "Stepping out with Spin". I have hooked up the stepper drive in a +ABAB- format on the terminal blocks, where AA/BB pairs are a coil (as indicated by a continuity test), and +- are supply voltage. For connections on the I/O to Propeller side, see the article. I measured how much current the stepper draws, and it turned out to be about 900 mA (at ~6.5v)·when in the continuous rotation mode (just spinning). When it was quickly changing dirrection the draw would pop up to about 1.2 A.

I tried it with a higher voltage (15 v) and a set maximum current draw of 600 mA (as specified by the L293D datasheet). However, when I turned it on, the voltage would pop down to about 5v, with current limited at 600 mA.

I also tried it with a physically smaller stepper, but it seemed to have the same draw.

Chris Savage

Are you using a Unipolar or Bi-Polar Stepper Motor? Please explain what wires are connected where…I am still not clear about the Stepper Motor connections.

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Chris Savage
Parallax Engineering

SRLM

The stepper motor that I'm using is a four wire (Bipolar, I think, but I'm not that familiar with steppers) The black and brown wires show continuity in a pair, likewise, the orange and yellow are a pair. I found a supplier for the motor here, it's titled "Minebea Printer Stepper Motor. (RFE)" and is third from the bottom. I've attached a picture showing my setup.The wall plug that I'm using in the photo is rated 9V 1A. When I measure it without load though, it's giving me 13.2 volts.