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From: David Wade <g4ugm@dave.invalid>
Newsgroups: uk.d-i-y,sci.electronics.design
Subject: Re: Current consumption of LCD kitchen timer?
Date: Sun, 11 May 2025 21:40:08 +0100
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On 11/05/2025 20:45, john larkin wrote:
> On Sun, 11 May 2025 17:51:56 +0100, Pamela
> <pamela.private.mailbox@gmail.com> wrote:
> 
>> On 17:15  10 May 2025, john larkin said:
>>> 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.
>>
>> I asked the question about current consumption because, when the time
>> is up, I leave my kitchen timer beeping until it cuts out. That's
>> usually a minute of beeping.
> 
> That sounds anoying. I use a mechanical timer with "extended ring" and
> sometimes want to drown it.
> 
>>
>> If this is done a couple of times a day, would the AAA battery run out
>> in an appreciably shorter time?
> 
> Wild guess 50 mA. A good (not Amazon) AAA is good for about an
> amp-hour, which is 20 hours of beeping. At 2 minutes/day, it 's good
> for roughly 600 days. Replace the batteries every year.
> 
> What are you cooking? My biscuits are critical. One minute over or
> under wrecks them. I set the timer to 15 minutes and start inspecting
> from there.
> 
> 
> 
> 
I think that the equipment to measure probably costs more that a years 
supply of batteries.....

Dave