# Difficulty in deciding battery requirements. I am using 64 A3144 Hall sensors connected to eight 74HC165 shift registers & 64 WS2812B LED strip

The image is just a basic representation. I am making a college chess project.

I was powering all this with my laptop using an Arduino Uno. I plan to introduce a 16*2 LED display and one ISD1820 with speaker which can run for four hours but, I need more power for this.

I came to know about using rechargeable lithium ion battery for this.

12V is a generally available Li-ion battery so I found the use of a buck converter.

I tried finding the draw current from their datasheets but I could not find this term in datasheets. Is it Icc or supply current?

Based on the assumption that Icc is the draw current I came to the conclusion that a Hall sensor needs Icc 9 mA, LED - 50mA, shift register (HC165) - 50mA, 16*2 LED display - 160mA, ISD1820- 50mA & Arduino - 50mA. Please confirm this.

To run them for 4 hours - 9 x 64 + 50 x 64 + 50 x 8 + 160 + 50 + 50mA = 4436 mA × 4 hrs = 17744 mA or 17.7 A is needed.

Should I look for a rechargeable li-ion battery pack of 12V with at least 17.7 A current supply which I shall connect to the buck converter before supplying current to the circuit? What else should I keep in mind?

Keep it simple and don't reinvent the wheel: buy a 5 V power bank. Cheaper, no effort on your part, guaranteed to work, meets regulatory requirements, has a warranty, and, most of all, safe.

• Then what about the current requirements of the circuit? The maximum output current is only 1A of such powerbanks. Will the citcuit still work? Apr 17 at 13:24
• You can always use two power banks, one each to power half the LEDs. And the power banks definitely do more than 1A. I have a cheap one with two outputs: 1A and 2.2A. Apr 17 at 20:11
• How to calculate the total current my circuit would need? I have explained my circuit in below reply Apr 18 at 10:52
• _How to calculate the total current _? Measure it. Apr 18 at 21:05

"Based on the assumption that Icc is the draw current i came to conclusion that a hall sensor needs Icc 9 mA, led - 50mA, shift register(hc165) - 50mA, 16x2 led display - 160mA, isd1820- 50mA & arduino - 50mA."

"So to run them for 4 hours - 9 x 64 + 50 x 64 + 50 x 8 + 160 + 50 + 50mA = 4436 mA × 4 hrs = 17744 mA or 17.7 A is needed."

You've got some confusion in your units. Let's outline the procedure and principles involved.

There's no schematics currently shown in your question, thus no way to check the currents you quote.

So, taking your values as reliable for now, the currents drawn that you list are:

Hall Effect Sensor        9 mA
LED                      50 mA
74HC165 SRs              50 mA
LED display             160 mA
Speaker                  50 mA
Arduino                  50 mA
'Nice total' rounding     1 mA
------------------------------
TOTAL                   370 mA


If this is for a 5 V load, which at least your 74HC595s needs, then that's 1.85 W dissipated.

A buck regulator with a conservative 85% efficiency would then draw from a 12 V battery:

Po = 1.85 W / 0.85 eff = 2.18 W

Io = 2.18 / 12 = 182 mA


At first glance, for four hours this would need a 12 V battery of 728 mAh.

Now let's derate the battery by 50% to ensure well-powered operation near the end of four hours and to allow for the cells aging.

So that leads to a 12 V battery of 1092 mAh min. supplying a switch-mode regulator to drop the supply to 5 V and whatever other rails you need.

• I have added an schematic for better clarity. The image is just a basic representation. 7 more shift registers are connected to this shift register (shown in the image) and sensors are connected to these SRs similarly. Also 64 leds of a strip are connected in series to the same 5V supply. Though I would be using a battery as a source of power. Is your answer regarding my query still valid? Because i am using multiple sensors and leds. Apr 17 at 18:35
• Also, since in chess there are 32 pieces then i would be using maximum 32 sensors at a time. In LEDs also not all will be required to glow all the time just for few seconds maybe 10-15 sec because they glow only to tell possible moves. Apr 17 at 18:49
• @DhruvRastogi, the answer starts Let's outline the procedure and principles involved so I won't be going through your circuit and trying to calculate its power budget :-) I can't as only you know how it behaves, when it accesses I/O and so on. This answer shows how to take the currents you do come up with and produce a battery rating. I calculated the rating in a very different way to what you'd done and mine's 4% of what yours, before derating. What I can't do is track changes in your question and revise and revise my answer tutorial-style because it's a Q&A site, not a discussion forum. Apr 17 at 18:53
• Thanks @tony for this wonderful explanation. I get it clearly. Apr 17 at 19:00