Easiest way to create 1A constant current, for 4 lead ohm memsurement

[jase_31]

What is the easiest way to get a 1A constant current (using a battery) so i can measure the resistance of a long length of cable using a 4 lead method and my existing multimeter.

I need to put 1 1A constant current (like a bench supply)  - but fed from a battery (18560) or USB battery pack

I have seen Youtube videos that provide it with a LM314 and a resister. There are a number of power modules on ebay (usually based on the LM2577

Can I use something like a Step-down-Power-Supply-Module-5-32V board, that is designed to as a charging circuit.
https://www.ebay.co.uk/itm/DC-DC-CC-CV-Lithium-Converter-Step-down-Power-Supply-Module-5-32V-to-0-8-30/353167381042?hash=item523a6a9232:g:GOIAAOSwK2hfMlPS

[bob91343]

To measure resistance, a constant current source needs to be stable and accurate.  I don't think there is an easy or cheap way to do that.

Why do you want to reinvent the wheel?  There are many 4 wire Ohmmeters available, some at very low cost.

Alternatively, you can pour some current through and use the voltmeter-ammeter method to determine resistance.

[Gyro]

Welcome to the forum.

This Maxim battery operated App note circuit works well and has very long battery life (as long as you don't hold the button down more than is necessary to make the measurements). You can, of course, substitute the reference and opamp of your choice. It can be as accurate as your choice of reference and resistors.

http://www.wentztech.com/radio/resources/Projects/AN106.pdf

[ledtester]

This is a good video of what considerations go into the design of a milliohm meter:

https://youtu.be/anE0jDeBuxo

[NiHaoMike]

Make a sufficiently accurate constant current load and you basically have your answer.