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From: John S <Sophi.2@invalid.org>
Newsgroups: uk.d-i-y,sci.electronics.design
Subject: Re: Current consumption of LCD kitchen timer?
Date: Sat, 17 May 2025 19:40:14 -0500
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On 5/12/2025 12:13 AM, Paul wrote:
> On Sun, 5/11/2025 4:57 PM, john larkin wrote:
>> On Sun, 11 May 2025 16:32:03 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 2025-05-11 12:51, Pamela 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.
>>>>
>>>> If this is done a couple of times a day, would the AAA battery run out
>>>> in an appreciably shorter time?
>>>>
>>>
>>> I admire your patience.  That would drive me nuts.  I doubt that the
>>> beeper requires much current--piezo sounders are pretty efficient at
>>> turning battery power into annoying noises. ;)
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> Whoever invented the piezo buzzer should be welded into a prison cell,
>> with a dozen piezo buzzers.
>>
> 
> Does a piezo run off 1.5V ?
> 
> This sounds like alien technology.
> 


Nah. Bridge type drive using two port pins doubles the voltage. I've 
done it and it's been in a project in my house for about 5 years. Just 
checked and it still works. I check it every year. I drive it at its 
resonant frequency so that it makes max noise.