Stand Alone SX not working

Armored Cars

I am trying to make a stand alone SX but my computer won't recognize it, here is all I know to check so that maybe yall can help me track down the problem.

SX key itself works, as it recognizes the SX Tech board.

Have 5v reg, installed correctly, running off 4 AAs which are supplying a little under 6v.

MCLR tied to VDD with a 10K resistor.

Osscilator installed, grounded, and connected to chip and key.

SX Key inserted correctly, also connected to VDD and VSS.

Thats all I know to check.· Any help will be appreciated.

·

Jonb

Try removing the oscilator when programming. Some people devised various techniques like DIP switches, I suggest a 3 pin female header such as the one on the tech board.

Post Edited (Jonb) : 4/2/2005 4:01:35 AM GMT

Bean

When you say "my computer won't recognize it" do you mean you cannot program it with the SX-Key ?
If so you may need to disconnect the oscillator to do the programming. What type of oscillator are you using ?
Bean.

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"SX-Video Display Module" Available Now.

www.sxvm.com

"A problem well defined, is a problem·half solved."
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Armored Cars

I'll try that. Im using one of the occilators that came with the SX Tech board.

Armored Cars

It still says there is no SX on COM1. I know its got the right port because it works with the tech board.

KenM

To clarify,

You are trying to program your SX without the SX connected to the techboard, is that correct?
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allanlane5

Yup, SX-Key uses the 'osc1' and 'osc2' pins to program your chip, and then uses those pins to run your chip under the debugger. It keeps full control of your chip clock while it is plugged in. This won't work at all with a native oscillator plugged in at the same time.

KenM

Allan and others,

You can program the SX with the resonator installed, where I call a resonator the following...

http://www.parallax.com/detail.asp?product_id=250-04050

I have successfully programmed my SXes several times without removing the resonator.

However, you cannot debug with the resonator installed, as Allan mentioned.

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Armored Cars

I have a Tech Board that works, but I am trying to program an SX that is not on the Tech Board. I have the resonator removed (even though the Tech Board programs even with it in). The SX connected to OSC1 and OSC2 but it still says "SX Key not found on COM1"

Bean

You do have Vdd and Vss to the SX-Key connected as well right...
Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"SX-Video Display Module" Available Now.

www.sxvm.com

"A problem well defined, is a problem·half solved."
·

Armored Cars

Yes, checked it with a meter on both the chip and the key.

kb2hap

You have it all hooked up like in the attached picture correct?



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DTQ

Armored Cars

Yup. Ill get a pic tommorow, maybe you will see something I am missing. Right now its too late.

Bongo

You will have exactly this problem if there are not enough currents. The key seems to require quite a lot. In the configuration you have indicated, the SX will probably work, but not with the key.

alkaline cells deliver current from 0.8 volts to 1.5volts, with a reasonably linear drop over life. A 7805 regulator require 2 volts min. headroom. 7 volts minimum in, for 5 volts out.

Simple check, remove batteries and hook up a 1 amp, 7 volt + supply

David B

Maybe the problem is the voltage.

I have a handmade SX project board that is powered directly from 4 AA NiMH cells. When the NiMHes are fully charged, they show about 5 volts, and I can program the SX fine. But after a few hours of development, when the NiMH voltage sags below about 4.5V, the SX program won't detect the SX anymore. The existing program in the SX still is able to run, but evidently the SXKey requires pretty close to 5 volts to run properly. I charge up the NiMHes, and I'm back in business.

Try measuring the voltage at the chip. I've tried running a 7805 from 4 alkaline cells and had trouble getitng 5 volts out - the 7805 I used needed about 6.5 to 7 volts in to give a reliable 5 volts out.

David

Bongo

Although there is less voltage differrence between a charged and a flat NiMH compared to an alkaline, there is still enough to make inclusion of a regulator a good idea.

There are LDO (low drop out) variants that only need 1 volt headroom.

If power consumption is not an issue, you can just use more cells, and let the regulator waste the extra voltage for a charged pack.

For battery power only, I would now use 2 cells and a step up (boost) switching supply. This allows use of bigger batteries (D cells have more amps/$ than smaller cells), and full use of the battery ie run it down to 0.8 volts. However, board design/sheilding for emi do become an issue.

bongo

David B

I would agree with you in some cases but not necessarily all the time. It depends on the specs of the parts.

My project uses an SX and a Garmin GPS receiver, both of which have very wide (although slightly different) specified input voltage ranges.

While programming the Sx, it seems that a regulated supply would help, but in standalone operation, it is completely within the specs of the parts to run under a wide voltage range.