You did

At this point I'm contemplating sacrificing

you more then likely supplied them with sacrificing 5 volts

Code:

Part Number VCC Range Page Size Temp. Ranges Packages
23K256 2.7-3.6V 32 Byte I, E P, SN, ST
23A256 1.5-1.95V 32 Byte I P, SN, ST

When you have computers that cant stream video whats 8 mhz micro controller going to do? 

There to things that cause that error one the reset didn't happen and two you didn't set the com port.

If it's a uno I would make sure I had the com port set right.

Well what i see is poorly made boards plus a bug or two and things start to fell. The bad soldering show up I've pulled power transistor off a board the solder not even holding them. buttons the same thing. Reflow the board and it works like new. It't just poorly made stuff now days.

Bugs do all kinds of things to boards I fix about 50 boards a year in stoves, dish washer and microwaves. And bugs are the number one killer. That and the fact that most newer stuff is made poorly.

Why not just use fan thats on the oven. With the right timing it should work fine just figure when to turn off the heat but leave the fan on

The way I posted was at the emitter side which should work fine the one you
Posted is not going to have the range your looking for

For starters you setup is totally wrong you want to feed the ptoto transistor with a 100k resistor VDD to collector and tap the  ADC to the emittor with a 10k resistor

 

Serial is bit shifting, But we really need the op to post more info about it like what chips is on the board.

What chip is on them a max serial driver i bet DIN is data, load is latch and CLK is Clock. But you'll need to see what chip there using may even be a shift register.

There to kinds of test one to see how long the battery last and two to see if the battery is good.

To see if a battery is good doesn't need a big load to see how long a battery last and is still good the user load would be a better choice.

Testing a  Nicad with a 6 ohm resistor 1/2 watt would be like short not last not very long because the Nicad can dump out amps when shorted needs a 3 watt resistor.

The fact that the v.reg output drops from 12V to 2V means you do have a serious load on

He is floating the inputs and the zener diode set's the motor voltage.

So if your feeding 12 your burning off half of it some where

I would set up the test circuit http://www.datasheetcatalog.org/datasheet/sanyo/ds_pdf_e/LB1641.pdf

Have you seen this https://itunes.apple.com/us/app/get-console/id412067943?mt=8&ls=1

The iPad Camera Connection kit let's use USB to serial adapters.

Na the op is using the regulator as a current source and if you read the data sheet on most they lower the voltage to hold there output of current. I posted this before but some people don't read data sheet's  and think that A plus B is C Na A can be A LOL.