AXE091 Mod - Grief Saver !

H

Hydroid

Senior Member
Hi All,

Did a quick search, but didn't see this so...

Here's a quick, easy mod, that can save a lot of grief. I have the AXE091 development board, which has a single 7 segment LED on it. It is pinnned out to a header WITHOUT current limiting resistors. I also dabble in Basic Stamp and have their development board which has five 7-Seg LED's - but their board HAS resistors.

So, I figured that before I blew the display, I would add resistors. A dremel tool cutoff wheel slices the perfect slot between the connections and leaves just the right gap to solder in a surface mount resistors. While I was at it, I did the servo signal line as well (not shown in photo) since all the docs I have call for a 300 ohm resistor there too. I didn't have 300 ohm, but I did have 330 ohm. They work just fine.

They're so small that it took some time with tweezers and my magnifying headset, but it worked out great. Much less risk now of releasing the magical blue smoke that makes solid state devices work ;)

Regards, John.
 

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E

eclectic

Moderator
Very nicely done!

Put it in the Finished Projects - miscellaneous,
to make it easier to find in the future.

e
 
hippy

hippy

Ex-Staff (retired)
Neat solution.

I believe the reason there aren't resistors included is the extra board space required for a DIP package or the extra assembly step for SM resistors. Both would deliver small gains for some but would push the cost up quite severely for everyone.

Another possibility could be to cut the connections to the common cathode legs and insert a single resistor between those and 0V. This isn't as good as individual series resistors for each LED anode but would be an easier option and even a lowish value R would offer some degree of protection, though not necessarily enough for all cases.

The issues with using a single resistor are that brightness dims the more segments are on and if Vforward across the LED's differs it may be that some won't light when others are on.
 
H

Hydroid

Senior Member
hippy said:
I believe the reason there aren't resistors included is the extra board space required for a DIP package or the extra assembly step for SM resistors.
Click to expand...
That's most likely true. The Parallax board is madeup totally with surface mount components, so it only makes sense that they would place resistors in their design.

I've been having issues with a clock design (discussed in another post) and have traced the troubles, by use of an external RTC board, to the RTC section of the AXE091. Per the DS1307 data sheet, a ground plane is called for undereath the timing crystal, as well as a ground ring around the crystal pins and pins 1 & 2 of the DS1307. The AXE091 has neither of these. I can't say 100% if this is my issue, but once I determine how, I see another mod coming...

Regards, John.
 
M

MPep

Senior Member
Although not a Finished Project, and I certainly agree with you, in that part of the Forum there are far fewer posts so will therefore be alot easier to find for others in the future. :D
 
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