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RAMBo version 1.2 released
05 Oct Posted by johnny
UltiMachine is excited to announce some new developments. After months of design and testing, revision 1.2 of our flagship 3D printer controller board RAMBo is in production. Early batches have been tested by some 3D printing experts for several months and the verdict is in. It is ready!
RAMBo revision 1.2 has hardening additions to protect against a whole new level of the potential failure modes. As usual, this is the culmination of our work here at UltiMachine and from the RepRap Open Source Hardware community. More below...
The other exciting news is that Arduino is selling our products in The Arduino Store at Maker Faire Rome. You can buy the new version of RAMBo this weekend if you are lucky enough to be at Maker Faire Rome 2013! It is a great honor to have Arduino sell our products. Our (and most of the modern 3D printer control systems) are based on Arduino tech and the awesome path they have helped pave for Open Source Hardware. They also have a few other great UltiMachine products in their store. Stop by the Arduino Store at Maker Faire Rome to pick up your RAMBo, RAMPS, filament, and stepper motors. Version 1.2 of RAMBo will be available on UltiMachine.com October 11th.
Improvements for version 1.2 of RAMBo motherboard include:
USB isolation - Ground loops are a known issue with USB. When two devices are connected to mains power it is possible that their grounds are at different voltages. When a USB cable is connected between two devices with a different ground reference the cable can be a path for current return. This can cause interference, and in worst cases burn traces/components on circuit boards, and melt USB cables. It can usually be avoided by ensuring USB connected devices are plugged into the same power outlet as their peers. We opted to add isolation between the atmega32u2 that handles serial comms and the atmega2560 that runs the printer. The Analog Devices iCoupler ADUM7441 used is transformer based so it is isolated in a way similar to ethernet. We chose this part over opto-couplers mainly due to its small footprint for the number of isolated channels.
Thermistor over voltage protection - Over voltage and ESD damage to microcontroller ADC pins has killed many 3D printer controllers. Like many recent 3D printer developments a solution was proposed on the RepRap Forums. Bobc, Nophead, Cefiar, and NoobMan proposed an overvoltage protection for the thermistors. I found the discussion and based my implementation on nophead's sketch here. We customized it for the impedance, leakage current, and VCC level of RAMBo. It protects the Atmega2560's ADC from continuous 24V input and short pulses of 35V.
All the power rails on the new RAMBo boards are compatible with input voltages up to 35V.