EBay and Actuality

A project log for Digital Holga

Conversion of a Holga 120S to digital format with SD card output.

AnthonyAnthony 02/20/2015 at 01:371 Comment

As part of a number of posts I plan to write on this issue, while I have generally found EBay to be an excellent resource for certain, quality, inexpensive parts, purchased from a reputable seller (which would cost much more if purchased in the states-- presuming you are willing to 'wait' for the 2-3 week shipping times), it still never 'hurts' to take the provided datasheets with a certain curious 'grain of salt'.

Almost all the camera modules available, even from different manufacturers, are fundamentally quite similar, both in communication, data transfer, and structure (all topics I am looking to get into more detail later).

Another common similarity they share is typically some form of on-board voltage regulation, usually to bring things down to the typical 1.8 today's CMOS sensors use.

In the datasheet I was provided with the item, max input voltage was listed as 3.3V. Curious, however, I decided to locate the regulator on the board and look it up (Note: Your regulator on any specific Mt9d111 module from various vendors may differ, and thus it is worth double checking and looking it up).

In this case the regulator provided is the AMS117 (datasheet) from Advanced Monolithic Systems. A quick glance shows this regulator is rated at a max of 15V.

And so, moral of the story though the provided EBay datasheet suggests only 3.3V max power (which the Teensy provides), a look at the actual hardware says this would be powered quite fine by a 5V source from an Arduino type board or similar.

Always check out what you actually have in your hand-- It may turn out to perform better than you think.


Jarrett wrote 02/20/2015 at 17:04 point

Worth noting that in your case, 5v is probably fine, but not all devices that use the AMS117 will for sure work with higher voltages.

An example would be many high current applications. Linear regulators such as the above just drop voltages across them, without doing anything clever with storing energy. That means that if you power 1.8v with 3.3v input at 1A, then you're putting 3.3 - 1.8 * 1A = 1.5W across that little tiny chip. That might be okay, but if you supply 15v to the input, then it's 15 - 1.8 * 1A = 13.2W, which might let out the magic blue smoke.

This is also dependent on heat sinking/thermal transfer and ambient temperature.

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