The BeBoPr plus plus Changes - modmaker/BeBoPr GitHub Wiki
2014-02-09 Moved text from original page to this (separate) page.
BeBoPr++
Overview of changes between BeBoPr and BeBoPr++
This page gives an overview about what has changed and some features that haven't, comparing the new BeBoPr++ with the BeBoPr+ (or the original BeBoPr with added Bridge).
Board layout
The BeBoPr++ has gotten a complete new board layout. All SMD components were moved from the bottom side to the top side. There are no longer components underneath the board, reducing the overall board height and reducing manufacturing costs.
The choice of components makes it no longer possible to solder the board without specialized tools (e.g. a re-flow oven). As the board was never officially offered as DIY kit, this should not be an issue.
Elevated BeagleBone mounting
With the BeBoPr Bridge, the distance between the BeagleBone and the BeBoPr was increased. This allowed access to the serial console connector on the BeagleBone as well as the USB host port, the HDMI connector and the uSD card slot while mounted on the BeBoPr. This feature was propagated into the design of the BeBoPr++. Extended pin-header connectors create a similar gap between BeBoPr++ and BeagleBone.
Wide input power range
The step down converter has been re-designed to operate with a DC power supply that outputs a level in the range from 12 to 24 Volts. It's still using the same (proven) step down converter as before but some of the components have changed so that it now can operate at up to 24 Volts.
More power for heaters
Since the input supply voltage is also used for the heater PWM outputs, it's now possible to generate more heat (power) without exceeding the maximum allowed currents. The input power connector has also been replaced by a type that allows up to 16A of continuous current (instead of 12A). Now it is possible to power a heated build platform and an extruder simultaneously without exceeding the maximum current specifications.
Single fuse
The expensive and hard to get SMD fuses on the three PWM outputs have been replaced by a single 5×20 mm fuse. This fuse is now placed in the board input power line.
Input power LED
A green LED located near the input power connector indicates the presence of supply power and an intact fuse.
I2C connector
The BeagleBone's secondary I2C bus is now routed to a 4 pin connector, no need to solder wires directly to the board any more. This allows I/O expansion or connection of a simple I2C LCD. A level shifter allows connection of either 3.3 Volt or 5 Volt powered devices. No chance of damaging the BeagleBone when connecting 5 Volt devices. And automatic isolation of the bus when the external device is powered down prevents boot problems for the BeagleBone.
Emergency Stop input
The BeBoPr now also has a hardware emergency stop (ESTOP) input. Activation of the ESTOP signal negates the I/O enable without depending on the software. The ESTOP immediately disables the PWM outputs and stepper signals. A red LED signals the ESTOP state.
If preferred, the ESTOP signal can be configured to latch (remain active once asserted) until it's cleared by software negation of the I/O enable signal. Closing a jumper on the BeBoPr activates the latch.
The ESTOP signal should connect to a normally closed contact or some open collector / open drain type sensor. When not used, a jumper replaces the sensor. An external opto coupler / isolator can be used to interface to 24 Volt signals.
Improved PWM outputs
The PWM output stages have been redesigned to generate less heat in the output switches (FETs) and now allows 40 kHz PWM switching frequency without significant losses. The TO220 FETs have been replaced by SMD parts with very low RDSon. The 'heated-bed' output now can deliver 120 Watt (10 A) at 12 Volt, and even 200 Watt (8 A) at 24 Volt. Most heated build platforms can now connect directly, without the need for an external mechanical or solid state relay.
Each PWM output now has an on-board (fast recovery) free-wheeling diode. These diodes protect the FETs (and the rest of the board) from voltage spikes that occur when switching at high speed or when using inductive loads.
Furthermore the PWM outputs will now also work properly with very light loads. There is no biasing through the indicator LEDs anymore.
I/O enable LED
This LED indicates that the I/O devices are 'live'. As an inadvertently de-activated I/O enable disables the steppers and PWM outputs, this indicator is a necessity. A disabled enable caused by a software fault of overlay issue was not always obvious, and hard to track down, now this signal's state is directly visible.
Larger bypass capacitor for stepper modules
The bulk capacitance that bypasses the stepper motor power supply has been increased. A high quality 220 uF/50V electrolytic capacitor has been added to the board. This should prevent damage to the Pololu stepper driver modules caused from over-voltage spikes generated by the motors.
Reset button
The reset button has moved to the opposite side of the board. It's now located next to the power button.
Sensor power
The 5 Volts on the limit sensor input connectors is no longer controlled by the BeagleBone but available as soon as board input power is present. This supply can be used for limit switches that need a 5 Volt DC supply to function (e.g. optical sensors or three wire industrial proximity sensors) or special functions that needs power when the BeagleBone is not present or has been powered down.
Analogue input protection
Since the very first BeBoPr, the analogue inputs have been protected against shorts to the power supply by a clamping circuit. The bypass capacitor of the shunt regulator in this circuit has been increased for better circuit stability.
Higher stepper voltage
All capacitors in the stepper driver circuitry have been upgraded to 50 Volt types. This allows safe use of stepper voltages at up to 36 Volts. In most cases the maximum voltage specification of the driver modules will be the limiting factor.
Colour
No longer the boring green PCB but now fully in line with the BeagleBone Black.
Features that haven't changed
Dimensions
The board dimensions and mounting hole pattern have not changed.
Connectors
All connectors have remained the same and are compatible with the original BeBoPr connectors. The locations on the board haven't changed either, making the BeBoPr++ a plug-in replacement for BeBoPr+ boards or BeBoPr-with-Bridge combinations.
The two new connectors, for the I2C bus and the ESTOP input, are located between the reset button and the stepper motor power connector, beneath the RJ45 connector of the BeagleBone.