Continuity Tester

An LED light will not show battery voltage nor the charged state of the battery. You'd be better off using a meter designed for that purpose. Even Harbor Freight cheap freebie multi-meters have that function

Unless you really want to re-invent the wheel:-

Amazon ₹573

Flipkart ₹225

It probably wont work. If you have a single cell, the voltage drop you can afford from charging batteries is about 0.2V. A LED definitely has a higher forward voltage drop that that.

Moreover, if it somehow gets to work, connecting batteries in series with different charge levels are likely to burn not only the diode, but also the cables. Listen to the wise and do not make experiments with batteries if you do not know what you are doing for your own safety.

Universal Battery Tester ‑ For AA ... $6.99 Walmart Free shipping

Sir, I live in India, here continuity tester is sold for 0.5$ by small cottage industry. The owner is my friend. He just asked me about technical feasibly, so I thought of our friends in CR4.

That missing detail was very important. Answers would have been very different, had the forum known that up front.

Oh well.

$1.62 on Ebay

I doubt if they'll ship to India at that price: perhaps Suresh could let us know.

This is the best price I could find on ebay India

380 Rupees is about $6

I still think FlipKart (₹225) is his best option.

But we still really need to know if he just wants a battery tester, or, wants the fun of trying to design and make one.

Randall,I will send detailed pics shortly. Its local price is Indian Rs.36/- approx. $0.50. Thanks.

Mr.Randall, I have taken pics on my mobile I am not familiar with transferring on my P.C.Pl suggest some way to send them to you. Thanks.

If your phone has a USB socket for charging you should be able to just connect your phone to a USB socket on your PC.

Do a search for a sync cable: the PC end should always be an ordinary USB "A" style, but the phone end will need to match your phone:

mini, .............micro, ........or type C

Type C is fairly new, and is "vertically symmetrical" so that you can insert it either way up (which is great for oldies like me who can never see well enough to work out which way to insert).

Your charger may already have a sync cable which just plugs into the wall plug.

When you connect your phone to your PC, it should automatically connect and offer you the option to retrieve pictures or browse the folders.

You can see two external "drives" here, one is my internal phone storage, and, the other my SD card.

You can try "import pictures and videos", but, I always "open folder to view files"; then DCIM, and camera

Just select the images with the correct date and time and copy them to somewhere sensible on your computer.

Of course it's a good idea to do this with all your pictures because your PC screen is better to view them, and, you now have a backup.

If you have a google account associated with your phone it's even easier. You should only need to go into photos on your phone and select them to upload them to your account: on my phone there's a little picture of a cloud with an up arrow on it; sometimes it all just happens automatically. Then sign in to your google account on your PC then click on the little square of 9 smaller squares, and, select photos; choose the photo you want right click on it then save to somewhere sensible on your PC.

Good luck!

Thanks MrRandall.

I have downloaded pics and they are here:-

Hope you can watch all clearly. You can also see the price on the packet.

Thanks for helping me.

To simply convert a continuity tester to a "cell" tester is not a simple task. There are two major problems:-

1.) Continuity is an easy thing to measure, and, essentially is a YES/NO decision. I realise that a very low resistance might give a YES decision, but, when you're just trying to see where wires are connected that's not normally a problem.

Testing a battery by comparison is more of a continuous (unfortunate choice of word considering the context) measurement: look at the pictures of the testers others have posted links to. Some show a direct readout of battery voltage e.g. 1.32V; others show a needle which moves from a red area through an amber area into an increasingly green area.

2.) Look at the button cell in your existing continuity tester. I bet it's a special 3V cell (battery?) not a standard 1.5 volt cell. This is because nearly all LEDs have a forward voltage drop of greater than 1.5 Volts. Do a search of say Digikey for LED; out of ~22,000 results this is the choices you get if you want to narrow the search by forward voltage:-

there are lots of pages to scroll through.

So a single "test" cell will not provide enough voltage to forward bias an LED.

If you want to design a cheap battery tester for your friend I'd buy one of the existing ones and reverse engineer it. His skill is clearly in cost reduction of both material and production.

1. Agreed.

2.My friend is having cottage industry where his objective is to make something damn cheap but still serving purpose. His present product is well received in the market comparing the cost. It is bought by small shops or electricians who do small house appliance repairs. Product shown by others are good and long lasting,

3.Present product has 2 Nos. button cells voltage is not mentioned.

I will try to element these dry cells by shortening the wire connections and see what is the result.I will inform you regarding the same.

Just compare the cost, he is providing 2nos cells, 2nos plastic holders, cable, LED bulb for just $ 0.50.Still he has some profit.

Regards,

Suresh.Sharma

I have tested this unit without cells, I found it working good as battery tester. However i could test 2nos cells in series as it needed 3 v for lighting LED bulb.

regards,

Suresh Sharma

I built this at about the time of the thread but then got too busy at work to post it.

Just for fun I decided to design a cheap battery tester for AA type cells.

As I’ve said before the main problem is that LEDs normally have a forward voltage of greater than 1½V, so it’s necessary to make a very simple power supply to boost the output of the cell above the forward voltage of the LED.

This is a simple oscillator using two transistors as inverters with a 22µF capacitor on the output to “drive” the LED.

It’s drawn in LTspice so the components are not all shown as the ones I used for a prototype, or, the ones I would recommend if you wanted to produce it commercially.

Think of it like a simple CMOS oscillator

This is the LTspice simulation results showing the junction of C2, R5 and R4 (SumIn); The junction of R1, R5, R3 and Q1 collector (inv), and, The anode of the LED.

I made a quick prototype out of old (and probably not ideal) components lying about in the LAB.

Surprisingly it worked straight away at 1.5V but stopped working at about 1.3V. The original design had 470K in position R4: once I changed it to 100K the oscillator kept working down to about .8V

I only did the LTspice simulation later, it didn’t work at all with 470K but was OK as shown above with 100K.

This is a scope trace of SumIn blue and inv yellow

I took several pictures of the prototype with 1.5V, 1.4V, 1.3V etc.: it was easy to see the difference in brightness, but, it doesn’t show up in the photos.

If your friend decided to lay this out on a panelised PCB he’d easily get 100 units per PCB

The following are 100 off prices in US cents from Digikey India

Transistors Q1 and Q2

MMBT3904L RFG 5

Schottky diode D1

CTS521,L3F 12

22µF cap C1

C0805C226M9PACTU 13

LED D2

APHD1608LSURCK 20

All the resistors and the 100nF cap will be less than a cent each.

Thanks, it seems you have taken lots of pains in development of this device. I will pass

on full information to my friend and will come back to you.

Thanking you,

Suresh Sharma