Sx-tech board and miscellaneous wall warts...

tommy

why won't my SX-tech board run properly (read: "at all") when the wal-wart I just happen to use, is a 12-volt one...?·

my projects aren't fussy - well, yes they are... the motors won't faithfully turn on some of them unless I use the 12-volt one...

I can't imagine what might be "wrong" or different - but the SX-chip quickly heats up and the program inside doesn't start should I use a 12-volt supply by misteak.

My own SX's get only 5.1 volts from a 7805 regulator at the start of the circuit...·· Why is the SX-Tech board different ?· · Is there something that I should be aware of that would affect the operation of things that I build ?

·· thanks.·· tommy

Brian Carpenter

One thing that might be happening.... (this just happened to me and i called the great Guru Bean) When the sx starts up from the wall wart being plugged in, it takes time as the voltage 'ramps up' so therefore the sx tries to start but really doesnt have the voltage neccisary and locks up. Getting very hot. To remedy this i added BOR42 to the begining of my code. This tells the sx not to start untill it senses 4.2v

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It's Only A Stupid Question If You Have Not Googled It First!!

Sparks-R-Fun

Tommy,

I suspect that the difference has to do with the votage regulators being used. You will note that the SX-Tech board has an input voltage marking next to the power jack recommending 6-9 VDC. If I recall correctly (check before relying on this) the 7805 can handle much higher input voltages, maybe up to 30V or more.

Also, since wall warts provide unregulated power, their output voltage is very dependant upon the load placed on them. They will read higher on a voltmeter under a no-load condition and lower than rated under extreme loading.

Other things to consider might be the capacitors across the power rails and Brian Carpenter’s brownout setting suggestion.

- Sparks

tommy

originator's reply:

+++ aha ! -- thank you, Sparks...· you were right...

+++· the SX-Tech board uses an LM2940CT 5.0 volt regulator...· golly, they all look the same to me -- but unlike the familiar 7805, which accepts up to 30 volts input (and gets pretty warm while dropping the extra 25 volts), the spec sheet for the regulator on the tech-board states that the Max Input Voltage is "Iv=Ov+5" -- and the text states that it cuts out (for some sort of "safety" reason) (probably its own safety) when the input voltage exceeds that 10v level...

+++ so what I was seeing was normal operation.· and I must use a 6-9 volt regulator on the SX-tech board just like is printed on the unit.

+++ but I may indeed use a higher voltage wall-wart on my projects (which is capable of supplying·the needed,·higher voltage to my motors)...

+++ and I'm guilty of not following clearly printed instructions, and of that, "A-S-S... U-M-E" thing that we all do from time to time...

thank you,

· tommy