problem with dagu mini driver stopped working

[Alan]

Hi there,

Glad you made progress with this eventually. Please let me know if you have any further problems. Also, please feel free to email helpdesk@dawnrobotics.co.uk if you need a more timely response.

Regards

Alan

[hobbyrobots]

I don't have electrical engineering knowledge. Please help me to understand how to flash Dagu Mini Driver using Raspberry Pi 2 Model B without damaging any of devices.

1) Dagu Mini Driver can be powered from micro-USB and from Battery +/-. Near power switch it have V selector, which has two modes: +5V and Battery. From information on back side seems Battery = Vin? Seems I have default mode +5V and never changed it. How that comes that if I connect batteries to Battery + and Battery - and turn switch On it works even then V selector is +5V? Then that V selector does, that it is for?
2) In pi_isp guide there is instruction to level shift to +3.3V. I completely don't understand this. What device should I level shift to 3.3V: RPi or MiniDriver? How do I do level shifting?

[Alan]

Hi there,

Welcome to the forums.

In answer to your questions.

1. That jumper sets the voltage that is passed to the central voltage pin for the set of 3 pin connectors that run down the same side of the mini driver as the power switch. The default setting is to have +V=5V which means that all sensors and servo motors connected to those pins will run off 5V. For most situation this will be fine, but the problem is that the 5V is provided the the linear regulator on the mini driver which can provide a maximum of 1A current. In situations where you're connecting multiple servo motors to the mini driver that require a higher voltage, or which will draw more current then you have the option to run them directly off battery voltage by moving the jumper so that +V=+BAT. If you choose this option then it requires some care so that you don't damage your hardware, basically

• The maximum input voltage to the mini driver should not exceed 9V
• If VBAT is higher than 5V then be careful not to attach 5V sensors to those pins, you may fry the sensors

More information can be found in the mini driver manual.

2. When connecting the Pi to the mini driver. The Pi (running at 3.3V) needs to be protected from the mini driver (running at 5V). The easiest way to do this is to put 1K resistors on the connecting wires (as shown on the pi_isp page). This doesn't actually shift the voltage down. What it does do though is limit the current that flows into the Pi GPIO pins (I = V/R), the current is what would burn and damage the Pi. Now, this is a rather hacky solution, which has never caused me any problems, (I've flashed a lot of Arduino compatible devices like this using a number of Pis) but you may be uncomfortable doing it. If you'd like a proper level shifting solution, then I'd suggest using something like Adafruit's level shifting board.

Hope that helps, and gives you some useful information.

Regards

Alan