Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: john larkin <jl@glen--canyon.com>
Newsgroups: uk.d-i-y,sci.electronics.design
Subject: Re: Current consumption of LCD kitchen timer?
Date: Mon, 12 May 2025 12:53:39 -0700
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On Mon, 12 May 2025 19:53:14 +0100, Sam Plusnet <not@home.com> wrote:

>On 12/05/2025 15:20, john larkin wrote:
>> On Mon, 12 May 2025 10:55:50 +0100, Pamela
>> <pamela.private.mailbox@gmail.com> wrote:
>> 
>>> On 20:45  11 May 2025, john larkin said:
>>>> 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>
>>>>>>> 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 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.
>>>
>>> When I'm cooking the radio is on, the big extractor fan whirring away
>>> and the tap gets left running (yes!). So beeps from the timer add only
>>> a little more noise.
>>>
>>> That extra minute of beeping is useful when cooking something like
>>> pasta (or maybe a hard boiled egg) and you want to cook for just a bit
>>> longer.
>>>
>>> The question is ... is this truly wasteful on the battery or does it
>>> make little difference?
>> 
>> Use good batteries and replace them once a year. I do all mine in
>> January. Food is too important to take chances.
>> 
>>>
>>> I suspect a piezo buzzer doesn't emit repeated sets of beeps without an
>>> external chip, so the spec sheet may not contain the consumption info.
>> 
>> No, the piezo is usually a passive polarized ceramic strip, and the
>> driver is in the main timer chip.
>> 
>> When I get a new microwave, the first thing I do is open it up and
>> destroy the piezo. I don 't need a loud annoying BEEP BEEP to know
>> when the microwave is done. We kinda autistic engineers are triggered
>> by loud noises like that.
>> 
>> And I have a pretty good timer in my head, which some people do. I
>> usually know what time it is, within a minute or two. Quantitative
>> instinct.
>
>You are the exact opposite of my wife, who's signature phrase is:
>
>"Good heavens!  It can't be that time."

I once had a gf who was always between 1 hour and 2 hours late. 
I've never had a watch but I'm basically never late.

My wife tends to put things on a burner or into an  oven and go away.
I like her, so I keep an eye on things when I can.

I tend to design control systems by fiddling in Spice, instead of
using hard stuff like control theory. I can usually guess R and C
values pretty close, and iterate from there. Bad guesses can fail to
converge, the "lost in space" effect.