Path: ...!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: John S 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 Organization: A noiseless patient Spider Lines: 68 Message-ID: <100b9jo$l37m$1@dont-email.me> References: <36uu1k9dnlnle60okphglgqdnb9i88umgg@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sun, 18 May 2025 02:28:41 +0200 (CEST) Injection-Info: dont-email.me; posting-host="31eb6b91115e1c311bb541d308d681a3"; logging-data="691446"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/iRYrwYAeCaapNc+cCaJGX" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:Q9qTeHTnX4RP0Zm4ixWcliyuoBI= In-Reply-To: Content-Language: en-US Bytes: 3747 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 >> wrote: >> >>> On 5/10/2025 9:58 AM, john larkin wrote: >>>> On Sat, 10 May 2025 14:37:40 +0100, Pamela >>>> 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. > >