# Battery replacement for battery-only Igaging DROs?



## homebrewed (Sep 25, 2020)

I've got 5 Igaging remote-reading DROs on my mini machines (three on my mill and two on my lathe).  They can only use CR2032 batteries, and they all seem to eat them quite rapidly.  I have stacks of dead batteries waiting to be recycled.  I got fed up with continually swapping them out so initially modified one of my DROs by opening up the controller and soldering wires to the internal power and ground connections, then connected them to a battery holder with two D cells.  D cells have a MUCH higher mA-Hr rating than CR2032's.  Unfortunately, the extra wires (and perhaps the slightly lower supply voltage of 3.0V vs. 3.3) caused the position readout to become extremely unstable due to noise pickup.  I had traded one annoying problem for an impossible one.  I also didn't like the necessity of modifying the DROs in order to  hook up the external power.

Thinking about it some more, I realized that the USB connector brings out Vcc and Gnd (to power the sensor on the scale).  So I could access power and ground by making a little board with a male USB connector on one end and a female on the other.  The male would plug into the controller and the female would accept the cable from the sensor.  An external (noisy) supply line would be conditioned by a pi topology RC filter on the board.  Much cleaner, and a way to do it without modifying the controller. PCBs are so cheap now that the whole thing would pay for itself fairly quickly.  Not to mention the reduced annoyance factor.

This idea seems so obvious (in retrospect) that I'm wondering if anyone else has tried it, and, if so, how it worked for them.  Even if their solution involved just opening up the cable and soldering wires to Vcc and Gnd, I'd like to know.


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## AGCB97 (Sep 25, 2020)

I've been switching a lot of my things over to use Li-on batteries. The 18650 is about 4 volts when fully charged. There are all kinds of cheap voltage regulator modules in any voltage you want. Some are adjustable. So my stock pile of parts contains battery holders for 1-4 cells, regulators in most common voltages, and a good 2 cell charger with all the safety cutouts (over voltage, over current over temperature and maybe a few more  OVERS)  oh yes and a bunch of batteries. Start with one of each and if you like them then buy in quantity.
That's just my take.
Aaron


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## markba633csi (Sep 26, 2020)

Ferrite snap-on filters might work there, or toroid cores from an old computer power supply.  Florescent lighting could be one culprit
-Mark


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## homebrewed (Sep 26, 2020)

markba633csi said:


> Ferrite snap-on filters might work there, or toroid cores from an old computer power supply.  Florescent lighting could be one culprit
> -Mark


The main source of EMI is the mini mill's motor controller.  I could see the DRO readout numbers' wild fluctuations settle down as soon as I turned the motor off.  I did try shielding the motor cables -- only a slight improvement;  and a snap-on filter on the mill's power cord -- no improvement.  Shielding the DRO cables produced a noticeable improvement but did not completely cure the problem.  Electrically Isolating the scales from the mill did nothing. 

The best results came from a combination of inserting an RC filter in each sensor's Vcc connection, shielding the DRO cables, and hard-wiring the scale bodies to their respective DRO grounds.  The last step seems counter-intuitive, because it introduces a ground loop; but it worked for all 3 DROs.  Even with all this, on occasion a DRO will STILL go nuts.  That's a sign that the batteries in that particular DRO are starting to go flat.  I think low supply voltage decreases the circuit's noise immunity, so that's another reason to go with an external supply. I will design the supply to include battery backup in case of power failure.

I suspect the hardwired ground approach worked  because the scale is made from aluminum, which readily forms an insulating oxide skin.  The sensor (sender?) has a sliding contact to connect the scale to its internal ground (I ohmed it out to verify this) , but if it's highly resistive the scale can bounce around, electrically speaking.  Since the sensor uses capacitive coupling to read out its position, this is a Bad Thing.  One way around this would be to use the more expensive stainless steel rules -- no oxide skin to interfere with the sliding contact.  If/when any of my current DROs fail, I will replace it with the stainless steel version.


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## markba633csi (Sep 26, 2020)

So the EMI is coming from the motor controller directly through the air.  That's a hard one to solve, you can't easily stop it at the source.
I didn't know about the oxide skin issue, kinda sucks 
-M


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## homebrewed (Sep 26, 2020)

markba633csi said:


> So the EMI is coming from the motor controller directly through the air.  That's a hard one to solve, you can't easily stop it at the source.
> I didn't know about the oxide skin issue, kinda sucks
> -M



Yes, I've found it a difficult nut to crack.  The oxide skin problem is an hypothesis, but it appears to be consistent with the solution I found (pretty much in desperation ).

For additional confirmation of the oxide skin theory, I have two DROs installed on my mini lathe (it also uses a PWM style motor controller).  I bought them after I solved the DRO problems on my mill, so they DO use the stainless steel scales.  Initially I had some noise problems with them, too; but just implementing the inline supply filters took care of it.  No additional shielding or external connections to the scale.  They still eat batteries pretty fast so if my external supply idea works I'll install the external adapters for them, too.  

BTW, implementing the inline filters did require some board surgery.  I cut the Vcc trace, inserted a 1K resistor and installed a 1uF cap to ground on the other side of the resistor.  The sensor draws at most 70uA -- that's if it draws the lion's share of current, which likely is not the case.  So worst-case there's just a 70 millivolt drop across the 1K resistor.  The RC time constant is 1 millisecond so it's not filtering out 60 Hz noise -- just the higher frequency stuff coming from the motor controller.  But that appears to suffice.


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## RJSakowski (Sep 26, 2020)

A different setup as I am using the iGaging scales with the Touch DRO.  I  had EMC problems with my lathe motor when the motor was switched off.  I tried a number of solutions and finally end up soldering bypass capacitors across the power leads  in the pickup heads.  That solved my problem.


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## addertooth (Sep 26, 2020)

A ten microfarad tantalum capacitor soldered at the DRO end of your run should fix your induced noise problem.  Keep in mind that tantalum caps are polarized, so get the plus and minus connections right. Tantalum capacitors have VERY low impedance, and they snub stray signals quite well. 

As someone said, and 18650 lithium with a low drop out (LDO) regulator can work, or a disposable 3.3 volt lithium battery can work too. The disposable 3.3. volt cell will not require a regulator.  Even a 3.3 volt disposable which is half as long as a AA battery should give you a run time at least 30 times longer than your existing CR2032 button cell.


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## homebrewed (Nov 16, 2020)

I finally got my power adapter boards in and built one up to see how it works.  It didn't power-up the DRO at all, so I got out my DVM and did some measurements.  I won't go into all the stuff I did, but I discovered that the particular DRO I chose to test my battery replacement scheme draws _much_ more current than the one I initially used to "vet" my design.  I'm talking about 70 micro-amps for your average Igaging DRO, but THIS one draws 1.5mA!!!  OK, it is probably defective -- but the darn thing works fine if it has a power source that is stiff enough to provide that current.  Of course, that kind of current draw translates to short battery life -- but that's what I've been dealing with all along.

The bright side is that my USB jack/plug connections are OK.  I built up a second board but bypassed the filter so it was hardwired to the 3.3V power supply, and that one worked just fine.

So version 2 will use a board-level power supply regulator to condition the voltage going into the DRO.  At this point I can't return the deviant DRO so, since it is working OK other than the supply current problem, that's the most expedient solution.  10 PCBs are less than $10 in total so it also is the cheapest.

One issue I ran into with this project is that, as far as I could determine, all inexpensive USB plugs are meant to be used in a USB cable assembly, so they're not compatible with a PCB.  I looked at the plug dimensions and figured out that, at least for the older-style mini-B connectors used on my Igaging DROs, I could mount a cable-style jack if I used a thinner PCB and added cutouts on the PCB to accommodate the housing body.  At least that part of the project worked OK....

Fortunately, the PCBs were really inexpensive so I'm not out much, other than time.  And for a hobbyist that's OK.


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## AGCB97 (Nov 17, 2020)

Were the PCBs you used 'off the shelf' or special made? If special, from where?
Thanks
Aaron


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## homebrewed (Nov 17, 2020)

AGCB97 said:


> Were the PCBs you used 'off the shelf' or special made? If special, from where?
> Thanks
> Aaron



I designed the PCB myself.  I used EasyEDA, which is a web-hosted EDA system.  It has plusses and minuses.  On the plus side, it's free (with caveats), has a fairly large part library, and, since it's browser- based it can be used with just about any computer operating system.  It's got an autorouter but I didn't like the result when I tried it.  You get some choices w/regard to board color and thickness, which was useful when it came to adapting the cable-specific USB jack to my PCB.  They have a "cutout" feature that also was quite handy in that regard.

Negatives are:  the PCB manufacturer is in China so delivery times can be on the slow side; and the free version doesn't allow private designs (that's the caveat I mentioned), so any EasyEDA user can view your designs.  That doesn't mean they could use your design -- if you don't include any comments it could be pretty difficult to figure out just what it's for!  If you take this route make sure you have your own notes so YOU can figure it out .

You can use your own PCB design S/W like Eagle, or KiCad  to generate Gerbers that you can send to their PCB manufacturer.  That way you can protect your IP a little more, but still get really inexpensive boards.


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## homebrewed (Nov 17, 2020)

The high current consumption I observed appears to be related to the display.  When I press the "off" button on the display box the current goes down to a few micro-amps.   It doesn't totally power down because it maintains its position information as long as the batteries are good.  Unfortunately, those scales don't have an auto-power-off feature, so to maximize battery life on this one it really is necessary to turn it off.

When I first measured the current draw, I now recall that I did it on some newer scales I'd gotten for my lathe.  So it's possible that all my older scales (currently installed on my mini-mill) draw about 1.5mA.  Time to do some more measurements....


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## homebrewed (Nov 17, 2020)

Measurements have shown that all of my older-vintage igaging DROs draw about the same current, ~1.5mA.  Kind of blows my simple RC filtering scheme out of the water, so I guess it's time to go back to the drawing board.  I knew there likely was going to be a version 2 of the board anyway....


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## markba633csi (Nov 17, 2020)

I like easyeda also, it's easy to pick up and has a good feature set.  It has a couple glitches
-M


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## homebrewed (Dec 10, 2020)

Here's a screen shot of my revised battery replacement board.  It uses a 3.3V voltage regulator (on the back of the board) to handle the wide variation in supply current on my DROs.  I added an LED + series resistor to front-light the DRO readout.  Right now the DROs are not well illuminated so it makes it difficult to read them.  $5 for ten boards (that's fifty cents apiece and includes silk screen on both sides, solder masks and through-hole plated vias!).  As before, the shipping cost more than the boards....


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## martik777 (Dec 10, 2020)

I will no longer buy any of those igaging DRO's, nothing but trouble. A real DRO is not much more $$$ at $140 for 2 axis and $180 for 3 axis.
New SNS 2V Display 5um Milling Lathe 2 Axis DRO Digital Readout and 0.005mm TTL EIA 422 A Digital Linear Scale Encoder Sensor|Level Measuring Instruments| - AliExpress


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## homebrewed (Dec 11, 2020)

martik777 said:


> I will no longer buy any of those igaging DRO's, nothing but trouble.


I hear you.  I messed around with mine quite a bit before I fixed their noise-susceptibility problem.


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## kcoffield (Dec 19, 2020)

RJSakowski said:


> A different setup as I am using the iGaging scales with the Touch DRO. I had EMC problems with my lathe motor when the motor was switched off. I tried a number of solutions and finally end up soldering bypass capacitors across the power leads in the pickup heads. That solved my problem.



RJ, what size was the cap and can you elaborate a little on exactly how/where it was installed? I have a similar problem described here:








						IGaging DRO EMI Problem
					

I just finished a restoration of an old family lathe and added many upgrades. Among them was a three-phase motor with VFD and two iGaging Absolute DROs. The build thread is here. https://www.hobby-machinist.com/threads/new-caretaker-of-two-12-craftsman-lathes.87335/ I can be pretty handy with...




					www.hobby-machinist.com
				




Best,
Kelly


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## homebrewed (Dec 19, 2020)

I put 1uF caps in my read heads and they helped a lot but did not completely solve my particular problem.  Neither did some more extensive circuit board surgery where I inserted a resistor in the Vcc line to implement a filter.  I had to cut a trace on the circuit board to do that, not something everyone wants to or is able to do.

I'm curious as to what RJ did, too.


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## homebrewed (Dec 19, 2020)

Version 2 of my battery replacement design seems to work OK -- the DRO powered up and doesn't exhibit any problems w/regard to noise pickup.  Here's a photo of the assembled board, including the mini-B USB receptacle and jack:



The diode is to prevent damage to the adapter and DROs if the external voltage source is accidentally connected backwards, and also prevents transients from discharging the 1uF capacitor on the input side of the regulator.  While the latter might seem to be overkill, in fact I have observed DRO behavior that could only occur if the voltage to the sensor has been driven close to ground by external noise pulses.

Doing the same thing for newer DROs that use the micro-B connectors is a bit more challenging, at least as getting a board-mounted micro-B usb jack goes.  I had to get creative with what I could get for mini-B jacks -- they seem to be designed to be used as part of a USB cable, not a PCB.  In this case, I figured out that a couple of board cut-outs would allow me to install the metal shell so I can solder it to the board for mechanical strength.  The shell MUST be used to fully implement the USB jack so it's not an option to just toss it.

As I mentioned in an earlier post, I also have included a resistor so I can illuminate the readout with an LED.  The LED would be on the end of a pair of solid-core wires that can be bent to aim the light at the display.

One thing I noticed is that the weight of the USB cable hanging on the end of the board applies some force to the USB jack.  I need to do some cable management to address this.


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## RJSakowski (Dec 19, 2020)

kcoffield said:


> RJ, what size was the cap and can you elaborate a little on exactly how/where it was installed? I have a similar problem described here:
> 
> 
> 
> ...


I used a .05 mfd ceramic disk capacitor in parallel w2ith aa 10 mfd elctrolytic capacitor.  I picked up the 3.5 volt trace at the USB socket and the ground trace sround the middle of the circuit board.  I thought that I had a photo but I haven't been able to find it.


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## homebrewed (Dec 19, 2020)

If your sensor is the same as mine, Vcc and Gnd are clearly marked on the circuit board.  I tried to find a photo I took for someone else fighting a similar problem but came up short (it was awhile back).


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