Re: Current consumption of LCD kitchen timer?

On Sat, 10 May 2025 18:16:19 -0700, KevinJ93 <kevin_es@whitedigs.com>
wrote:

On 5/10/25 9:15 AM, john larkin wrote:

On Sat, 10 May 2025 10:56:01 -0500, John S <Sophi.2@invalid.org>
wrote:
 

On 5/10/2025 9:58 AM, john larkin wrote:

On Sat, 10 May 2025 14:37:40 +0100, Pamela
<pamela.private.mailbox@gmail.com> wrote:
>

I'm interested to know the current drawn by a kitchen LCD digital
timer.
>
(1) How much current does the timer draw when counting time?
>
(2) How much current is drawn when the piezo buzzer is sounding?
(Averaging out beeps and silent bits.)
>
My guesses are 2mA and 25mA, respectively. Is that about right?
>
>
I mean a timer similar to this one, running off a 1.5V battery.
https://www.amazon.com/Digital-Kitchen-Timer/dp/B00GOPICNM

>
That suggests a product line: a series of batteries (AA, AAA, 9v) that
measure current wirelessly, or datalog.
>

>
>
Hey! I like that idea!

 
A small PCB could have a tiny lithium battery and a uP with an
internal ADC. A diode would make a logarithmic current-to-voltage
converter from picoamps to milliamps. May as well report temperature
too.
 
Someone could sketch a schematic to discuss. It needs the right uP and
some code. And some mechanical design.
 
Might not handle high peak currents, amps.
 
Of course the electronics could be in a box with a tiny flex running
to the dummy battery. Or just squeeze the flex between the battery and
a contact. Or just sell the flex, with banana plugs on the other end
to go into a DVM. That's too easy.
 

>
There are a few products already available to easily do such
measurements, such as:
>
https://www.joulescope.com
>
This can also provide the time integral of consumption to be able to
predict battery life. It can be especially tricky where devices have
microamp quiescent currents together with multi-milliamp bursts when active.
>
If a meter shunt is large enough to measure the sleep current it can
have too large a voltage burden when the device springs to life -
accurate measurement of microvolts across the sense resistor is required.

A diode can make a logarithm of the current. Add an opamp to make a
zero-drop diode.

>
I have measured sleep currents with an ordinary DVM fairly successfully
by putting a large electrolytic across the terminals to avoid the large
drop during the active times.
>

Kind of expensive.