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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 19:29:04 -0500
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On 5/10/2025 8:16 PM, KevinJ93 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

Great! How you gonna fit it inside the timer compartment?
> 
> 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.
> 
> 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.
> 
>