Hello AAC,

A small two LED blinker circuit was built from
this schematic.

For testing a five-volt adapter was used to confirm operation. Because the circuit is part of wearable
badge it is planned to power the circuit with a coin battery holder which holds two 2032 3 volt coin
batteries.
When the batteries were inserted the battery holder was tested and the DMM showed 0.013 volts
instead of the 6 volts expected.

So I reconnected the 5 volt adapter to make sure something
about the DMM was amiss. But the DMM then read 5.1
volts.
There is a switch on the battery holder so I tried moving the switch.
When I moved the switch the result was 0 volts so I moved the switch
again and the reading went back to 0.013 volts.
I tried turning the coins upside down in the holder. This
gave a reading of -0.013 volts.
The battery holder came in a pack of ten so a second holder
was tried with the same result.
I tried holding the DMM probes against one of the bare coins
and got a reading of 3.3 volts.

Is there something about these battery holders I don't understand?
They seem like pretty simple devices so I am stumped as to
why I cannot get them to work.

Thanks

Allen Pitts

 

That's a bad circuit design as It has no resistors to limit the LED currents, so may draw a high current from the battery.

But you should read a higher voltage then 0.013V, so there seems to be some problem with the battery holder, which I can't surmise from the lack of information you've given about the battery holder or how the batteries go into the holder.

 

Have you tried reversing only one of the batteries?

 

Internet schematics have errors. So do my schematics.
Reverse C and E on Q6.
Added two current limit resistors for the LEDs.

 

Have you tried measuring the cell voltages without the holder?

 

in this case (3.7V supply) those current limiting resistors should be 100-220 Ohm. as long as Vf of LEDs is lower than battery voltage, i would rather connect the coin cell batteries in parallel to keep the voltage low (and current limit resistors low). otherwise there is no benefit of second battery - current limiting resistors would need to be larger (470Ohm or so) and still simply burn more energy for nothing.

btw that is just oddly drawn astable multivibrator. this is how that circuit is usually drawn
https://www.electronics-tutorials.ws/waveforms/astable.html

 

Is there something about these battery holders I don't understand?

One cell should be + side up, the other should be + side down. Check the holder for moulded marks indicating polarity.

 

hi Allen
Clip:
The insertion polarity for a CR lithium coin cell (such as CR2032, CR2016, or CR2025) follows a universal rule: the smooth, flat side marked with a plus sign (+) is the positive terminal, and the textured or smaller side is the negative terminal.

General Insertion Rules

• Positive (+) Side Up: In most standard slide-in or snap-in coin cell holders, the positive (+) side faces upward (toward you or the device cover).
• Negative (-) Side Down: The textured negative side faces downward, making contact with the metal spring or flat terminal pad at the bottom of the compartment.
• Sideways Slots: If the device has a slot where the battery slides in sideways, ensure the (+) symbol matches the (+) engraved on the housing.


How to Insert It Safely

1. • Check the compartment: Look inside the device's battery slot. You will typically see a small "+" sign stamped into the plastic or a metal spring contact at the bottom.
   • Match the contacts: The metal spring at the bottom of the compartment is meant to touch the negative (textured) side of the battery.
   • Place the cell: Slide the battery in so that you can still see the smooth face with the text and the "+" sign looking back at you once it is installed. [1, 2, 3]

 

Hello crutschow, EletricSpidey, ronsimpson, Alec_t, panic mode,
ericgibbs,

I must admit to being a bit red-face about not seeing the tiny
polarity markings inside the case that confirm the
point that ElectricSpidey and Alec_t made: The
coins are inserted one coin positive up and the second
inserted positve down. Not sure why assumed that both
coins would the same polarity up.

Now reading 6.6 volts.

Thanks.

Allen Pitts


PS The schematic recommended by panic mode
https://www.electronics-tutorials.ws/waveforms/astable.html
does look better.

 

bit red-face

One thing good about the internet, I can't see the color. We all have been there.