Quote:
Originally Posted by mrbigh
WOW, it's really tiny....  |
It's 1.5" by 1.75". There is no wasted space, and it doesn't cost a lot to make.
That's our May 2011 board. We've learned a bit and improved it since then, but there hasn't been a motivation to have new boards made.
We spent quite a bit of time on the layout and made a few compromises to keep all signals on the top layer. The bottom layer is entirely a ground plane.
The left side is the "quiet side" with 8 analog inputs. The top three have resistor dividers for higher voltage signals.
The right side has four outputs, driven by two dual MOSFETs in SO-8 packages. The MOSFETs are logic level drive and are rated at 9.1 amps per channel.
Each input and output has the same three pin layout. Pin 1 (always on the outer edge) is a ground, pin 2 power and pin 3 the signal. Six of the analog inputs have 3.3V power (for temperature sensors and throttle), with the bottom two have 5V power for the current sensors. All of the MOSFET-driven outputs have 5V power.
Since the ADC has a 3.3V maximum input, we orient the current sensors so that increasing current drops the output voltage: zero current has a 2.5V output dropping to about 1.0V at maximum current.
The four pin connections in the middle are the motor PWM output (ground, +5V, and both low and high side signals) and a SWD program/debug header. We program using a ST-Discovery development board which is well under $20.
The motor controller is voltage isolated from the chassis ground, and it uses an isolated gate driver. That gives us the option of changing it to be traction voltage referenced, or just leave it fully isolated for safety.