SX-48 Proto Gone?

JDOhio

I have been working with a SX-48 protoboard for a while and tonight, I received the Vpp generation error message out of the SX-Key. I tried the SX-Key on another SX-48, and the error message did not appear.

After reading through other posts and comparing voltages between two SX-48 protoboards, the one difference that stands out is OSC2 measures 4.8 volts with no resonator and no SX-Key. I'm thinking that this is bad. Any suggestions?

Thanks,

Joe

JDOhio

I was reading the post started by dave_f (Can't get the debug to work, all the buttons are greyed out (http://forums.parallax.com/forums/default.aspx?f=7&m=252891)) . As I read it, I recalled something that is a probable cause. I had lifted the output pin of the 5 volt regulator so that I can drive the board with 3.3 volts. For programming, I use 5 volts using a jumper between the lifted pin and a one pin header in the board. I accidentally touched the jumper to the raw input of my voltage adapter and the board LED lit briefly. After reading the post, I suspect it's possible that the small surge affected the SX-48.

As an aside, I was in a mild state of concern when a supplier said it might be week before backordered boards would be available. The Parallax availability is 26 Mar. I found two other sources and each of them had three boards in stock.

The Hobby Engineering web site indicates some are in stock but I did not confirm it.
Electronics Express (http://elexp.com/tst_5300.htm) had three (I ordered two).
Abra Electronics had them on backorder.
HVW Electronics (http://www.hvwtech.com/products_view.asp?ProductID=620) had three.

Joe

Post Edited (JDOhio) : 3/1/2008 12:08:06 AM GMT

LoopyByteloose

JDOhio,
March 26 is not far away. I've been thinking about getting a few SX-48s.· The problem ins Debug appears to have been a faulty OSC connection within the SX-Key [noparse][[/noparse]cold solder joint], not a power problem.

Parallax provides a device called the Key-Ring for programing 3.3v devices in circuit. I have one and it is quite handy. It provides the +5 to the SX-Key while isolating the 3.3v system for operation in Debug at 3.3v.

You don't have to mess with leaving the 5 volt regulator in place and jumpering. You can swap it out for a LM2940-33, but you have to change the related capacitors to have proper function of the low-drop out regulator. Or you can remove the regular and use the holes to install a couple of pins to connect directly to a battery supply.

The SX-48 has several features that are not well known, but interesting. The WDT can be adjusted for much shorter turn around than the SX-28 an·the two 16 bit multi-use timers have the ability to trigger the Interrupt Stack [noparse][[/noparse]if you need to] in six different pathways.

So, if you really want low power, long battery use - 4 AA NiCads with work from 4.8 volts down to·2.6 brown out and the Sleep mode·can extend that use greatly.·A multi-use timer can trigger a wake up from a longer interval.·You don't need a regulator in such a set up as a regulator will merely use 10ma/hr when doing nothing.· Just make sure other components are geared for a 5v to 3.3volt range.· You can have the SXes comparator shut it all down at 3.3volts and avoid the brown-out point if the other components are not viable below that.

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···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Post Edited (Kramer) : 3/6/2008 1:07:08 PM GMT