Voltage feeding DRO “usb” digital scales?

[Norman PinkneyParticipant @normanpinkney15518]

Hi all,

I'm hoping someone out there can help. I'm looking for the voltage supplied by an Arc Euro digital display head to the linked scales. The scales take a 3v cell but the clock/data signals are only 1.5v. I would like to know what the voltage supplied by the head to the cells is – when operating in remote read? Does anyone know? or have a set of these they could measure for me – thanks. These are the links to the scales:

https://www.arceurotrade.co.uk/Catalogue/Measurement/Standard-Digital-Readouts/Standard-Digital-Readout-Bars—Horizontal-100mm-to-400mm-Length

And

https://www.arceurotrade.co.uk/Catalogue/Measurement/Standard-Digital-Readouts/Standard-Digital-Readout-Bars—Vertical-100mm-to-300mm

Any and all info on the voltage fed down from the Digital Display Unit much appreciated. Thanks in advance.

[Norman PinkneyParticipant @normanpinkney15518]

Any know the voltage supplying these DRO linear scales?

[Robin GrahamParticipant @robingraham42208]

Hi Norman. The potential between pins 1 and 4 on my unit is 1.7V. I think that's the supply with pins 2 and 3 clock and data.

Robin.

[Les Jones 1Participant @lesjones1]

I have always supplied this type of scale with 1.5 volts when using home made remote displays. I think you will find the remote power connections connect directly to the internal battery contacts. The recommended silver oxide cells are rated at 1.55 volts when new. I have used an LM317L to provide the 1.5 volts supply from the 5 volt rail for the logic in my remote displays. Although USB connectors are used on these scales they DO NOT use USB protocol.

Les.

Edited By Les Jones 1 on 01/07/2020 09:10:19

Edited By Les Jones 1 on 01/07/2020 09:25:05

[Robin GrahamParticipant @robingraham42208]

Les, the ARC scales in question use CR2032 (3V) cells – I think the OP wanted to know if the remote unit just replaced that voltage or supplied 1.5(ish)V direct. The latter seems to be the case.

Robin.

[Les Jones 1Participant @lesjones1]

Hi Robin,
I have some digital calipers that use CR2032 cells but the data output is still 1.5 volts. I think they have a built in regulator to drop the 3 volts down to 1.5 volts.

Les.

[Norman PinkneyParticipant @normanpinkney15518]

Gents,

Many thanks for the rapid and detailed responses – exactly the info I was looking for and it is much appreciated.

Regards, Norman

[Robin GrahamParticipant @robingraham42208]

Posted by Les Jones 1 on 01/07/2020 20:28:00:

Hi Robin,
I have some digital calipers that use CR2032 cells but the data output is still 1.5 volts. I think they have a built in regulator to drop the 3 volts down to 1.5 volts.

Les.

Hi Les. This is interesting! Well, to me as someone with little knowledge of electronics anyway. The ARC readout unit can be powered from the mains via a 6V output 'wall wart', or from two internal AAA cells in series, so about 3V. But it puts out 1.7V, so there must be a regulator in the unit which can drop either 6 or 3V to 1.7. Then it presents the 1.7V to the scale, which anyway must have a built in regulator to drop 3V to 1.5. It all seems a bit over-complicated! Can you explain why it's done like this?

Norman – apologies for hijacking your thread, but I'm trying to get to grips with the same stuff myself – glad your question has been answered,

Robin

[AdrianRParticipant @adrianr18614]

Robin,

The chipset used in the senors is designed to run from battery e.g. in digital callipers. For low power consumption, you need to use lower voltages and smaller components in the ICs.

Examples of low voltages for power saving are the voltage on phone CPUs is below 1V, the latest ones about 0.7V and PCs are about 1.3V.

Adrian

[Les Jones 1Participant @lesjones1]

Hi Robin,
I started using Chinese scales with the Shumatech DRO350 many years ago. There was a lot of discussion on the Shumatech forum about jitter on the displayed values when the scales were supplied from the DRO 350 rather than their internal button cell. A few of us traced this to the fact that there was a section of PCB track between the 1.5 volt regulator and the negative connection to the scales that also carried the negative supply to the multiplexed LED display. The multiplexing current caused a small amount of voltage ripple along this section of track which was enough to cause the readings from the scale to jitter. This showed that the scale reading was effected by variations in the 1.5 volt supply. So I think adding the regulator reduced the sensitivity to battery voltage variations. Also using the CR2032 increased the battery life.

Les.

[Alan Wood 4Participant @alanwood4]

Follow up on Les's comments I also did some work on the Shumatech which I wrote up here. This involved making a small 1.5V regulator 'pod' using the AMS1117 three legged regulator which is a really nice device. You can buy a ready made module for this from EBay. Search on AMS1117.

I also managed to build the same circuit inside a physical replacement of the battery but this was severe eyestrain.

Alan

[Alan Wood 4Participant @alanwood4]

Sorry forgot to say that the AMS117 is available in various fixed voltages including 3.3V to replace the CRxxxx cells.

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