Driving motors and powering sensors with the Baby O

I’m looking at building a simple robotic platform using Pololu’s chassis kit (with the Tamiya gearbox) and a Baby O, but wanted to check my understanding of a few things first. There’s nothing less fun than ordering a bunch of parts, hooking them up, and them promptly frying a chip because you misunderstood something.

I saw that this motor was recommended for use with the Tamiya kit and the Baby O, but just wanted to check that the Baby O can drive two of these motors (at around 5 to 8 volts) without damaging itself.

My other question is about the regulated 5V output on the Baby O. The documentation mentions that attempting to draw more than 100mA at 5V can damage the regulator. I looked up the datasheet for the regulator used and it appears that it has the same 100mA rating. How much of this 100mA is typically consumed by the Baby O itself while driving motors (by the ATmega and the motor driver)? Have you thought of providing another version of the Baby O which can provide more current (or simply upgrading the regulator on the standard Baby O)? It seems like that would be a valuable improvement that would not increase the cost significantly.

Also, has anyone had any experience powering the Ping sensor offered by Parallax off of the Baby O’s regulated output? It’s datasheet says that the maximum current drawn is 35mA, but I know ultrasonic sensors often draw brief pulses of high current, and I don’t want to fry the regulator by powering it straight from the Baby O. I can always add another regulator, but that is just more parts, and I’d prefer to avoid it if possible.



The Baby Orangutan will handle the motor you are talking about. The power consumption of the Baby O depends on what you’re doing with it, but it’s around 25 mA. If you’re regulating from a relatively low voltage (e.g. the 5-8 volts you mention), there won’t be too much power dissipation in the regulator, so I think an excessive load is more likely to make the 5V line drop than to damage the regulator.

Thanks for the feedback regarding the higher-current power supply. From our design perspective, the size of a larger power supply was a bigger concern than its cost. How much current would you like, and how much bigger would you tolerate the board being if it could achieve that current?

I think you can connect the Ping sensor without worrying about damaging the regulator. If you have access to an oscilloscope, it would be interesting to look at the Vcc line to see if there are any big glitches on it. If there are, you could add some capacitance (up to a few hundred uF if you can fit it in your project) from Vcc to ground to smooth out the power.

- Jan

Thanks for the feedback! That’s a good suggestion about checking out the Ping sensor with an oscilloscope. I hadn’t considered the size of the chip, and I certainly see why it’s a concern now that you pointed it out.

I’m just now beginning experimenting with robotics, so I still don’t have an excellent grasp on how much current many of the common sensors require, but it seems like 100mA could be quickly used up as a robot’s complexity increases. It may simply be necessary to add an external regulator to power the hungrier components, but it would be very convenient if it could be integrated into the Baby Orangutan.

While looking for the datasheet for the LP2981 I ran across the LP38691, which could provide up to 500mA, and appeared to be in a similar package. I didn’t examine the datasheet closely, so it’s entirely possible that this part would not be suitable for something like the Baby Orangutan, but having 500mA available would be very convenient. Without having used the Baby Orangutan I couldn’t say how much it’s small size matters, but I know for my purposes being slightly (say ~10% or 20%) larger would not make a difference.

Thanks again for your help, I’m looking forward to experimenting with your controllers!

500 mA is a lot, so no small regulator will be able to deliver that. The unit you mention only works to 10V, whereas we would like operation past 15V. Once you have a 13V input (e.g. from a 12V battery), regulating to 5V means an 8V drop, and at 500 mA, that’s 4 watts dissipated, which is well past what any small package can do. Switching regulators don’t have those kinds of losses, but they usually require some other components (inductors, capacitors) that add to the overall size. They keep getting better, though, and we’re using them in newer designs. For example, our newest Orangutan, the Orangutan SV-168, has a switching regulator that can deliver up to 3A. We’ll also be coming out with stand-alone switching regulator boards (we just released a 5V boost regulator) to make it easier to add these kinds of devices to your projects.

- Jan