Hi, I have two questions regarding the Zumo Robot for Arduino, v1.2 (Assembled with 75:1 HP Motors).
We are planning to control the Zumo with the raspberry pi only, but we want to use the zumo shield for its sensors. It seems that most sensors work on 3.3V, but there are some pull-up resistors which might only work for 5V.
Can we simply power the zumo board by the 3.3V GPIO pin from the raspberry pi and use 3.3V logic level for controlling the zumo shield from the Raspberry pi? (the reflectance sensor is the main sensor we use)
How many amps of current can be drawn from the 7.4V power booster? It would be nice to draw power for the raspberry pi from this and perhaps also the Arduino. What happens if I draw too much power if that is possible at all?
Using a Raspberry Pi with the Zumo Shield, chassis and reflectance sensor array (along with powering everything from the 4-AA batteries) is probably not very practical, since you would need a logic level shifter and you would probably need a separate 5V regulator to power the Raspberry Pi.
As an alternative, you might consider the A-Star 32U4 Controller LV with Raspberry Pi Bridge. This robot controller can be powered from 4-AA batteries and power the Raspberry Pi as well. It includes dual motor drivers and since it is Arduino-compatible, you should still be able to use it with the Zumo reflectance sensor array, or one of our other QTR reflectance sensors. If you are still going to use the Zumo chassis, mounting sensors might be slightly more difficult without the Zumo shield, but overall, the A-Star 32U4 Controller LV with Raspberry Pi Bridge is probably a much more convenient way to add a Raspberry Pi to the Zumo chassis.
Thanks for your answer. From the manual I read “the Arduino’s regulated 5V and 3.3V voltages supply power to the motor
driver logic” which means that not VBAT, nor Vin (7.45V) is responsible for the logic level, but the regulated 5V from the Arduino is.
So can we simply provide 3.3V from the raspberry pi on both the 5V and 3.3V regulated power pins? (This should make the logic level 3.3V)
Or are there other problems we might bump in.
It sounds like you are referring to the Zumo shield user’s guide. I looked over what you suggested (connecting 3.3V to the 5V and 3.3V pins on the Zumo shield), and I did not see anything obvious that might cause a problem. However, the Raspberry Pi needs to be powered from 5V, so you should not be using the 7.4V output from the regulator if that is the case. You might consider a separate 5V regulator such as the S7V7F5 5V Step-Up/Step-Down Voltage Regulator.
As I mentioned in my previous post, it might not be very practical to use the Raspberry Pi directly with the Zumo shield and sensors. For example, it could be tricky to get the reflectance sensors to work directly with a Raspberry Pi since they rely heavily on timing and the Raspberry Pi is not as capable of performing timing-sensitive operations as the Arduino. If you do not have the Zumo shield and reflectance sensor board already, you might try getting a QTR-1RC or QTR-3RC sensor first to see if you can get it working directly with the Raspberry Pi.
We have a step-down buck converter, so getting 5V is not really a problem. I see how the timing might be an issue.
I think instead it’s best for us to use the Arduino for controlling the Zumo and have the raspberry pi communicate with the Arduino over serial. The raspberry pi can then do the more computational stuff like image processing.
Thanks for your help!
It sounds like you are planning on using a 5V step-down regulator with 4-AA batteries. Please note that when discharged, 4-AA batteries will drop below 5V, so you might still consider a step-up/step-down regulator instead. With 4-AA batteries, you will probably have to consider the dropout voltage of your regulator, which will likely result in the output being lower than 5V.
You will probably need a logic level shifter if you are using an Arduino on the Zumo and communicating with it through I2C or TTL serial with your Raspberry Pi, but other than that, I do not see any obvious problems with this.
Is it safe to connect a 5v step-down converter to the Vin pin and use that to power the Raspberry pi and also use the Vin pin to power the Arduino? They will draw around 1A (combined). What is the maximum rating for the current that can be drawn from the power booster?
Are you asking about powering a 5V step-down regulator from the VIN pin of the Zumo shield and using that to power the Raspberry Pi? The voltage at the VIN pin of the Zumo shield is already stepped up from the battery voltage, so stepping that back down would be less efficient than just using a step-up/step-down regulator powered directly from the battery voltage. Also, the VIN regulator probably cannot handle that kind of current draw, especially with the extra loss of efficiency from multiple regulators in series.