Question
Asked March 22 2015

Community Question

I'm looking to implement a way where as the EZ-B moniters the LiPo battery voltage, it will trigger a script to say "Low battery. Robot is powering down" when the low battery warning activates, and proceeds to switch the EZ-B off, possibly triggering a relay so it breaks the connection between the battery and EZ-B, and then I can charge the battery without disconnecting it from the EZ-B.

The problem I run in to trying to figure this out is re-initialising the relay to re-establish the power connection, as I would need the EZ-B to operate the relay which at this point would be in its "Off" state so it wouldn't trigger the relay. I'm normally pretty good figuring this sort of thing out, but I can't get my head around this one.

Has anyone done something similar to what I'm looking to do? If so, I'd love to hear your solutions.
March 22 2015
How about something like a monentary switch push button. You press it and it bypasses the relay to power on the EZ-B which then sets a digital pin high to re-energize the relay and you can release the switch.

My only concern is how much of a battery life hit will you take keeping a digital pin high and the relay energized.

If you expect the robot to be unattended so fully discharging the batteries is a real worry, than probably worth figuring something out.

Alan
March 22 2015
I kind of had the same thought. Also, Never ever charge a lipo unattended. It always leads to bad things happening.
March 22 2015
steve G

rs media has this.he says all systems powering down or
the batt in my feet needs changing
DJ Sures
Synthiam
March 22 2015
Due to the compact size of the EZ-B v4, there is absolutely zero room left on the PCB for a battery power relay. If anyone has seen an EZ-B v4, it is probably the most compact PCB I've ever seen:)

As for powering down the EZ-B with a low battery, a solidstate relay can be connected to a digital port. Using EZ-Script, you can use the GetVoltage() command to get the most recent voltage from the EZ-B v4

Here is one from SparkFun, but it only does 8 amps - which is not enough juice for a Revolution robot: https://www.sparkfun.com/products/10636
March 23 2015
Thanks for the advice guys. I think you may be on to something Alan. Using a momentary switch to temporarily bypass the relay might be an option. Two reasons why I'm looking to do this, is 1) I don't want to manually disconnect and remove the battery every time it needs recharging, and 2) I would eventually add a auto dock and charge feature so this is where I would need the batteries connection to the EZ-B cut while it recharges.

I'm aware about the safety of recharging a LiPo battery unattended and I use a Ballance charger with an auto cut of feature which reduces the chance of "bad things happening".

The amperage is actually something I didn't fully take in to account while thinking about this so thanks for the heads up DJ. So it does look like a relay is the way to go. Just to be clear, when I was asking about the auto power cut off, I wasn't asking about having it added to the EZ-B, as you really have done an amazing job designing the v4 to be as powerful and as compact as it is, and know that adding a relay to the board to carry out this fiction would take up to much real estate. No, this is something I want to add myself for the possibility of designing a "dock and charge" on my current and future projects.

I suppose what I'm ultimately looking for is a convieniant and safe way to recharge a LiPo battery that is still connected to an EZ-B, much like a laptop or mobile/cell phone does (The device can still have the battery connected, and even be used). Maybe this could be a future EZ-Robot product module, that could be designed to connect to the EZ-B's power base connector that could be that could be added to the product range and sold in the shop. Just an idea.

But for now, my current project has a Roomba for a drive base, so when the LiPo gets to 6v or so a final script is triggered to say" I'm going to recharge", and send a "dock" command to the Roomba which I know how to do, then powers off the EZ-B as the Roomba seeks the docking station. Once I get this figured out Incan build on it from there.

Anyway thanks again for your input guys. :)