[time-nuts] 5 Digit Panel meters

[Tim Shoppa]

This all probably belongs on volt-nuts not here. But 16 bit ADS1115’s are common as dirt for a few bucks and will yield most of 5 digits of monotonic non-skipping counts.

The internal reference and programmable gain of the ADS1115 is 0.1% ballpark. So any implication that all 5 digits are accurate is of course bogus. It still is useful for a lot of high dynamic range applications that we used to do with log detectors.

Tim N3QE

> On Sep 7, 2020, at 1:21 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> So, *assuming* there is no other ADC on the board ….
> 
> DC performance of the STM8 ADC’s is somewhere in the 8 to 9 bit range as far
> as ENOB with significant averaging. For the sake of simplicity, let’s say they *do*
> make it to 10 bits. 
> 
> But … do we get the 10 bits?
> 
> The range on the meter is 33V. The reference to the DAC is (likely) 5V. You just lost
> nearly 3 bits from that scale mismatch.  At the 5V level, you would be running just over
> 7 of your (ideal) 10 bits. 
> 
> Net result is that you are trying to check a 16 bit gizmo with a not quite 8 bit device.
> 
> Bob
> 
>> On Sep 7, 2020, at 10:01 AM, DM <dgminala at mediacombb.net> wrote:
>> 
>> I must caution all who would buy the 5-digit panel meters, thinking that they are actually capable of accuracy that you would normally expect from a 5-digit meter. 
>> The panel meters in question use a STM8S003F3 micro-controller, which contains a single 10-bit A/D. Depending on which eBay or AliExpress listing you look at, accuracy varies from 0.3% to 0.05%. 
>> Make your own deductions from this info, just be aware that all is not what you might expect of this cheap little meter. 
>> 
>> Cheers, 
>> Dave M 
>> 
>> 
>> From: "Perry Sandeen via time-nuts" <time-nuts at lists.febo.com> 
>> To: time-nuts at lists.febo.com 
>> Cc: "Perry Sandeen" <sandeenpa at yahoo.com> 
>> Sent: Monday, September 7, 2020 12:20:12 AM 
>> Subject: [time-nuts] 5 Digit Panel meters 
>> 
>> Learned List, 
>> From the on and off list comments I've received I realize that I didn't provide a fuller explanation of my proposed idea for this I apologize. 
>> What I was proposing was to try and use the tiny panel meters fount on ebay when you use the category listed as *Digital Panel Meters*. One listing number is 203076543505. Measurement range: DC: 0.000-33.000V. for $3.83 plus free shipping. This is just one of many listings for similar items. As I stated in my original post, I have no idea if they are accurate, stable or suitable to what I proposed. 
>> Some of the replies mentioned temperature drift and other potential problems which may make then unsuitable for my idea. This was to measure three different voltages simultaneously and see if there was some useful correlation in the readings. 
>> This is an experimental concept idea which may or may not be useful..Sometimes these ideas work or we learn to go to plan *B, C, or D* 
>> Because of the low cost i felt that this might a useful idea. Others with more experience of these voltages and how much they do or do not change may judge my idea as impracticable. 
>> That's fine. 
>> 
>> I learn from the list comments and I'd rather hear that it's not a good idea from the members before spending the money and effort. 
>> I do have a Fluke/Phillips 6.5 for making precise reading when needed. 
>> 
>> Regards, 
>> Perrier 
>> 
>> 
>> 
>> 
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