# 6 Batteries With A Zumo? / Modding Voltage Divider [SOLVED]

I would like to attach an extra 2xAA battery case to the back of a Zumo to extend its endurance.

The nominal voltage of a NiMH battery is 1.2V

V = 1.2 X 6 = 7.2V

The problem is that a new and fully charged NiMH battery can go as high as 1.4V

V = 1.4 X 6 = 8.4V

Is this too much voltage for the Zumos voltage regulator to handle?
If you can supply the IC part number, then I can download the specs.

Thanks

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Hello.

That regulator boosts VBAT to 7.45V to power the Arduino through its VIN pin. Voltages above 7.45V are passed straight through the regulator, so you could use higher voltages like 8.4V. This voltage will show up on the Arduino VIN and on the Zumo reflectance sensor array, if you are using one. Note that the Zumo reflectance sensor array was intended to be powered at 7.45V; higher battery voltages will cause the IR LEDs to be brighter, which could affect the behavior of the sensor and could cause the emitters to prematurely burn out.

-Jon

[quote=“JonathanKosh”]Hello.

That regulator boosts VBAT to 7.45V to power the Arduino through its VIN pin. Voltages above 7.45V are passed straight through the regulator, so you could use higher voltages like 8.4V. This voltage will show up on the Arduino VIN and on the Zumo reflectance sensor array, if you are using one. Note that the Zumo reflectance sensor array was intended to be powered at 7.45V; higher battery voltages will cause the IR LEDs to be brighter, which could affect the behavior of the sensor and could cause the emitters to prematurely burn out.

-Jon[/quote]

Thanks Jonathan!

I plan to use an I2C sensor for line following so I’m OK with a Vin > 7.45V.

However as I am writing this I may have encountered another problem:

NiMH battery have a nominal charge of 1.2V
V = 1.2V X 6 = 8.4V X 0.66 (Battery voltage divider) = 4.79V

New and fully charged NiMH battery can go as high as 1.4V
V = 1.4V X 6 = 8.4V X 0.66 (Battery voltage divider) = 5.59V

According to the schematic I should be able to desolder one of the 2 parallel 20k Ohm resistors in the voltage divider changing it to a 1/2 voltage divider.

V = 8.4V X 0.50 (Battery voltage divider) = 4.2V

Can anyone please identify on of the two parallel resistors in the voltage divider for me please?

I am also open to other solutions if they are as simple a desoldering an SMD.

My current design specs require that I eventually use every available pin on My Uno:

• Servo with medium range IR and Ping mounted
• Short range IR rear
• Short range IRs lft and rht edge (maybe)
• PS2 controller
• External LED
• I2C line tracer (eventually)
• Motor encoders (only rht tread active, just to measure forward distance when autonomous)
• Zumo shield: batt voltage divider, compass for turns, and buzzer.

That’s why I need the extra batteries!

[quote=“SRS”][quote=“JonathanKosh”]Hello.

That regulator boosts VBAT to 7.45V to power the Arduino through its VIN pin. Voltages above 7.45V are passed straight through the regulator, so you could use higher voltages like 8.4V. This voltage will show up on the Arduino VIN and on the Zumo reflectance sensor array, if you are using one. Note that the Zumo reflectance sensor array was intended to be powered at 7.45V; higher battery voltages will cause the IR LEDs to be brighter, which could affect the behavior of the sensor and could cause the emitters to prematurely burn out.

-Jon[/quote]

Thanks Jonathan!

I plan to use an I2C sensor for line following so I’m OK with a Vin > 7.45V.

However as I am writing this I may have encountered another problem:

It seems that a 1/3 voltage divider and 6 NiMH batteries might exceed the maximum voltage tolerance of Arduino input pins.

NiMH battery have a nominal charge of 1.2V
V = 1.2V X 6 = 8.4V X 0.66 (Battery voltage divider) = 4.79V

New and fully charged NiMH battery can go as high as 1.4V
V = 1.4V X 6 = 8.4V X 0.66 (Battery voltage divider) = 5.59V

According to the schematic I should be able to desolder one of the 2 parallel 20k Ohm resistors in the voltage divider changing it to a 1/2 voltage divider.

V = 7.2V X 0.50 (Battery voltage divider) = 3.6V
V = 8.4V X 0.50 (Battery voltage divider) = 4.2V

Can anyone please identify, on the Zumo Shield, one of the two parallel resistors in the voltage divider circuit?

I am also open to other solutions if they are as simple a desoldering an SMD.

My current design specs require that I eventually use every available pin on My Uno:

• Servo with medium range IR and Ping mounted
• Short range IR rear
• Short range IRs lft and rht edge (maybe)
• PS2 controller
• External LED
• I2C line tracer (eventually)
• Motor encoders (only rht tread active, just to measure forward distance when autonomous)
• Zumo shield: batt voltage divider, compass for turns, and buzzer.

That’s why I need the extra batteries! [/quote]

Hi.

The resistors that you referred to are R10 and R11 on the Zumo shield. I have circled them in the picture below. Please note that the output of that voltage divider is only connected to A1 on the Arduino when the battery level jumper is on. If you do not want to use this jumper to measure the battery voltage, you should not have to change those resistors. If you do want to use that feature, I cannot think of a simpler solution than removing one of those resistors.

Also, I noticed that you quoted your earlier post, but then edited the quote to contain more information. I almost missed what you added, which was really helpful in understanding your question. In the future you might consider posting just the question without quoting.

-Claire

[quote=“Claire”]

Also, I noticed that you quoted your earlier post, but then edited the quote to contain more information. I almost missed what you added, which was really helpful in understanding your question. In the future you might consider posting just the question without quoting.

-Claire[/quote]

Thank you very much Claire!

Stupid mistake.
I quoted my own post in full with no comment… Dooh!

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