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January 14, 2007
about 9 years ago
This is a great breakout board but has a very cheap and insufficient parts; namely the voltage regulator and low voltage detector. The Atmega128 can draw up to 400mA of current but the voltage regulator on the board is a 78L05 (which only delivers 100mA). The low voltage detector is tied to the /reset pin the uController but the voltage detector’s trip point is MUCH to high (4.7-4.85) for battery power (especially if the regulator is only dilivering 100mA).
I found the following to fix the problem quite nicely:
1)Either replace the low voltage detector with one at a lower trip point or just rip it off completely (alot of people wont need it if they replace the voltage regulator).
2)Replace the 78L05 with at the very least a 7805(DOV 2v, 1A) but there are nicer regulators out there for 1$.
a)LT1129-5 @ 700mA with DOV of 0.4V. This chip has many protections including reverse polarity, current, temp, etc
b)TL750M05 @ 750mA with DOV of 0.6V. Same protections as the other but also Voltage Load Dump which is good to have with motors
A second note is to make sure that the regulator is giving you 5V. Some 5v regulators give 5.5v which the Atmega128 will happily accept but some programmers (that take power from the board) will not be very happy.
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