Assistance with EasyEDA PC Board software and JLPCB: finding stocked resistors for 5.4V Mercury Battery Replacement

ic-racer

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I'm working on modifying a PC board ( link to the regulator ) to output 5.4V for mercury battery replacement.

The issue at hand is the PC board is using SD8942 with two resistors to set the voltage. All fine, but my specific problem is as such:

I'd like JLPCB to make the board and install the resistors. To do this I need to locate the two resistors they have in stock in the correct size and put them in my EasyEDA project so they can install the resistors when they make the board.

The equation is: R1 and R2: V = 0.6 * (R1 / R2 + 1)



I need to make it output 5.4V



 
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ic-racer

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This is as screen shot of the original file in EasyEDA. Maybe it is just busywork, but I'm having trouble locating two appropriate resistors via the software.

Also, something as easy as changing the sliksreen so it no longer reads (88.9k and 110k) I have found frustrating.


 
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ic-racer

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As I work through the EasyEDA tutorial, I did find this statement that will help:

 

rwyoung

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Digikey (digikey.com) or Mouser (mouser.com) in the USA and then just add them yourself. Drop shipping them back to JLPCB is going to cost an arm and a leg for two parts that are going to be about $0.02usd in small quantity anyway.

They appear to be 0603 size. The 110K value can be had as an E96 or E192 (1% or 0.1%) value while 88.9K is not a standard value in either 1% or 0.1%. There 88.7% is closest. You can do the calculations based on nominal value and then test worst case for say plus or minus 0.1% on either value at room temp. Also, if you really want to be hardcore, factor in the tempco of the resistors and the operating range for your finished project. Or just get the 0.1%, solder them in and test it...

From digikey :
110K, 0.1%, 25ppm $0.15 each in small quantity (my comment for 2cents was assuming 1% and 100ppm) but this isn't a bad price.

88.7K, 0.1%, 25ppm also $0.15 each.

Given the shipping cost and absurdity of ordering just one tiny component, go ahead and order at least 10 each of hand soldering or 100 if you do plan to send them back to JLPCB for soldering. Still cheap component cost.

Rob
 

koraks

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ic-racer said:
(88.9k and 110k)
Click to expand...

Are you sure you're approaching this correctly?

From the SD8942 datasheet:

Vout = 5.4V
Vfb = 0.6V
It follows that R2 = (R1)/8 in your application.
If you take R2 = 15k and R1 = 120k you'll be right on the money and both values are E12 series, so common as muck.

The footprint on that board looks like something like 0603 or so. I bet you can get 0402, 0603 or even 0805 soldered onto those pads manually.

If you get an SMD resistor kit from e.g. AliExpress, you'll have values to match your application. Costs only a few bucks. 1% accuracy will be plenty good enough in all likelihood.
 

Nicholas Lindan

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JLPCB and PCBWay have common parts in stock. There is no need to supply them.

5% SMD resistors are generally better than 1%, I wouldn't worry about tolerances.

EasyEDA isn't the best choice of software to use. Try KiCAD, which is open source, or see if you can get hold of an old 'free' version of Eagle. Eagle limits the board size to 4x6" (? going by memory) in the free version.
 
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ic-racer

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Yes 0603.

Having the board made with no resistors in those slots is an option too. However, right now I can't delete the components from the project.

I did find out that the Library components (mentioned in post #3) show items not available and is not very useful.

The work-around is to search directly from JLCPCB for 0603 resistors in-stock and find the JLCPCB part # and type it into the Library search box. From there, one has access to a "Place" button to put the resistor where it needs to be on the layout.

However, as mentioned above, I can't seem to delete the existing resistors.

The Delete function here does nothing. I am getting closer, however.
 
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koraks

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ic-racer said:
However, as mentioned above, I can't seem to delete the existing resistors.
Click to expand...

I don't think you're supposed to.
The logic of most EDA suites I've used is that you use the schematic capture to select and connect components. Then in the PCB layout you do the physical routing. This means that any changes to components or nets should be done in the schematic capture, and then cascaded to the PCB layout. I've not used EasyEDA much, but I suspect this is how it's supposed to work there as well.
 
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ic-racer

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So, I'm 99% there. I have added the 120K and 15K resistors to the diagram. All I need to do is move them over to the correct locations after deleting the components (R1 and R2) in those locations. Can't seem to do that at this time.

 
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ic-racer

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Excellent, I did find the schematic ( on this site ) but it opens in a separate window. I CAN delete the resistors in the schematic.

Now, just to find out how to combine the schematic and the layout in EasyEDA...right now they are in two separate and unrelated windows.

 
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ic-racer

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BTW: I have used the on-line help for EasyEDA to ask these same questions too. Still waiting for a response, though I have come pretty far with just the suggestions here.
 

koraks

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Well, in this sense I have to agree with @Nicholas Lindan; EasyEDA certainly is 'easy' in terms of its learning curve, but project management is kind of crappy and confusing. Unless you have a complete project file (IDK of EasyEDA has something like that; I'd hope so), you're basically stuck with rerouting the PCB manually. You could use the original one as a template. Yes, crappy workaround, I know. I hope there's a better way, but no guarantees.

I personally prefer DesignSpark, but most people these days use KiCad. They're functionally comparable, but KiCad is open source.
 
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ic-racer

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Looks like the designer has posted over 150 open source projects all with with EasyEDA file, schematics and BOMs, so I suspect he knows the software pretty well to help me, if he responds.

 

Nicholas Lindan

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If all you are looking for is a 5.4V output linear regulator - is there any reason not to use a commercially available part - 5.4V TO-93 This is not a TO-220 package, but you may not need the larger package for the (I imagine) low current draw you require. This component was POOMA (starts with "Pulled"...) and I have no idea if this is the best selection or that this vendor is reputable.

* * *​

As Koraks pointed out - you have to modify the schematic to do what you want to do.

There should be a project file - the project file links the schematic and the PCB - you probably won't be able to do the linkage on your own. Often you won't be able to open a PCB file without the project and schematic files, or at least shouldn't be able to.

In laying out a PCB you start with the schematic, annotate the schematic with part values and package sizes (SOIC, 0603...), and then start the PCB editor.

If you can't find the project file, you may find it easier to start a new project, create a schematic and then create the PCB.

OTOH,

Packages that allow you to proceed with a 'naked' PCB file usually have a feature to 'unlink' the PCB from the schematic - try searching for this option. After that you should have complete freedom. Be sure to backup everything before doing this, results can be a bit unpredictable.

Along with the project file you may also need a library file that holds the definition of all the components. There are huge library files that come with PCB software. These libraries have lots of derivatives of 'standard' components and it is SOP to create a custom library file containing just the components and specific variants selected for the design. As you got this far without the board library the design may use unadulterated library definitions and you may not need this file.
 
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ic-racer

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BTW the project at hand is to solve the battery issue for the Horseman focal plane exposure meter that takes a mercury battery.

Actually this reference indicates 5.2V rather than 5.4V:

 
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ic-racer

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Again, I'll ask the creator for advice here, but on his site, the links the open up EasyEDA on-line version with the PC Layout and schamatic loaded. I have copied the links from his site below so you can see:

Here and Here.
 

Nicholas Lindan

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ic-racer said:
Layout and schamatic loaded. I have copied the links from his site below so you can see:

Here and Here.
Click to expand...

What happens if you click on 'project' in the upper left?

(I don't have an EasyPCB account, too many accounts already)

Things that are 'free' are the ones that cost you the most.
 
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Nicholas Lindan

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I'll take a flying leap of faith and postulate that your application will do just fine with a bog-standard 5 volt regulator.

I don't know what your primary power source is. If it is a wall wart then any regulator will work. If a battery then an 'LDO' (low drop-out) regulator will work down to a lower battery voltage and thus give you longer battery life.

Search the usual suspects - Digikey and Mouser.
 

Andreas Thaler

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I'm really relieved to not be the only crazy person here
 

koraks

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Nicholas Lindan said:
I'll take a flying leap of faith and postulate that your application will do just fine with a bog-standard 5 volt regulator.
Click to expand...

I suspect so, too.
"Worst" case scenario you connect a small Schottky diode between the regulator's GND lead and actual circuit GND (cathode to circuit GND, anode to regulator GND pin), effectively lifting it by about 300mV. This will make 5.3V or thereabouts.
 
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ic-racer

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Nice solution, worth a try. I actually have not yet opened the meter yet, but I presume there is plenty of free space in there.
 
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ic-racer

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I may have to revert to "Plan-B" and just use a stack of four zinc cells with a little adapter for the mercury 5.2/5.4V battery because I was not able to take the meter apart.

I'm stuck on removing the knob. The set-screw is out and the trim piece on the end is off. It appears the knob is frozen or glued on the shaft. I'm pretty sure a second screw holding the halves togeter is under the knob.

I might try wrapping the knob with a lot of tape and use a gear puller.

 

reddesert

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I have not used EasyEDA, but I have used Eagle. Other people have explained this, but I don't think it's sunk in. You are not intended to edit or add components on the PCB layout directly. You download the schematic, edit the schematic by replacing the components that you want to change, and then render the revised schematic into a PCB layout. I googled the help and in EasyEDA this should be done by "convert to PCB" : https://docs.easyeda.com/en/Schematic/Convert-to-PCB/index.html
 

Anon Ymous

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You need to remove the brass piece at the center. Safety pliers would be a choice, but lens spanner could also be used. That's what these 4 holes are there for.
 
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