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Convert an Electronic Bathroom Scale Into A Shipping Scale for <$1

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Picture of Convert an Electronic Bathroom Scale Into A Shipping Scale for <$1
Shipping Scale 1b Strike a Blow Scale.jpg
Shipping Scale 1c Cat On Scale.jpg
Shipping Scale 1a Floor Scales.jpg
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In my small business I needed to weigh medium to large items and boxes on a floor scale for shipping. Rather than pay way too much for an industrial model, I used a digital bathroom scale. I found it to be close enough for the rough accuracy I required when over 15lbs (7kg), as well it measures up to 330lbs (150kg). Way more than I can lift.

I was frustrated because the display was always hidden under the item I weighed. Sure the result locked in but only if you got lucky, blindly timing it right and quickly moving the box after.

I can also see a potential of this for persons with some physical challenges. Think about the hard of seeing reading at their feet, bad backs or spines making it difficult to bend to read the display, pregnant women who can no longer see the floor beneath them (Quit laughing before some big mama come slap you!), etc. I am just saying it could be medically difficult for some to see well to the floor level. It would be much easier for them to have the display at about face high?

So I wondered about why the display has to be stuck inside the bathroom scale and thus on the floor or under the item being weighed? I then realized that it does not when you see the inner workings of my electronic bathroom scale.
 
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Step 1: Tools and Stuff You Will Need

Picture of Tools and Stuff You Will Need
Shipping Scale 2b Tools.jpg
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I started with a very basic digital bathroom scale that I bought from my favorite Thrift Shop cheap. (I did not want to risk my own on my first convert.)

The scale I chose to do just happens to be made by EKS, it has a Silver color ABS platform over black metal base, LCD display, Capacity max 150kg (330lbs) and d = 0.1kg (0.2lbs), Auto shut off, Tap start, 9vdc battery.

Solder, Iron etc
Drill with small bit (3/32 inch)
Piece of 4-wire cable (telephone wire is perfect, look any Junk Store for <$1.)
Spring Hook
and of course duct tape, naturally! (What is a project without it?) In this project we do not use it but it is so handy you will want some anyway.

Step 2: Open Up Your Scale

Picture of Open Up Your Scale
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Orient the scale face up with the display away from you, as if you are about to use it. Consider the display then at north position.

Grip the sides, at the east and west and while clasping the top to bottom, flip over so only the north and south switch. Place it on workbench face down. Ok, you did not really have to clasp bottom to top yet, but get into the habit for later or you will say many bad words. I said some I did not know I knew.

Remove the battery.

This is a good time to remove the 2 screws securing the lbs/kg switch. If your scale is like mine.

The only thing holding my scale together is 4 strong springs. Unhook each, but note the orientation.

Now it is important to clasp together the top and bottom parts. Grip the sides, at the east and west and while clasping the top to bottom, flip over so only the north and south switch in one movement. Place it on workbench face up.

Step 3: The Guts

Picture of The Guts
Shipping Scale 4b Beam Corner.jpg
Shipping Scale 4c Beam Hanger.jpg
Shipping Scale 4d Beam to Stirrup.jpg
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Gently lift off the top, flipping over as you do, just in case there is any thing else connecting it to bottom. There was not on mine.

Before anything gets knocked out of place take special care to learn how the beams are hung on your unit. Also notice how the stirrup hangs the beams onto the load cell (actually it is a strain gauge, but lets not get too technical here). See next step for more pix of the interior.

Also take a close look at which direction the springs are hooked into the top plate. It is important, as they will fit both ways until you try to hook them up later. If you are careful with the flipping steps, they should remain hooked.

If yours is an older scale or dirty with dust bunnies you may want to disassemble the beams and clean up a bit.

Step 4: What If It's Too Late Or You Did Not Listen

Picture of What If It's Too Late Or You Did Not Listen
Shipping Scale 6d How was that.jpg
Shipping Scale 6c How was that.jpg
Shipping Scale 6e How was that.jpg
Shipping Scale 6f How was that.jpg
Shipping Scale 6b How was that.jpg
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So you either have a different style scale or you jumped ahead and missed a step. Now its all a mess inside.

If you want to see what it is like to forget to flip right, Look at these pix.

I don't believe it is possible to put it together this way. But it does help to show an underside view and to understand how things work.

Step 5: Wiring The Guts

Picture of Wiring The Guts
Shipping Scale 5c load Cell Wiring.jpg
Shipping Scale 5b Load Cell w Wiring.jpg
Shipping Scale 5d Run Cable Out.jpg
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Remove the display circuit card, switch and battery holder together.

You should see the display is wired to the load cell with 4 wires. Make a drawing of which color wire goes to which connection on both the card and the load cell.

We will replace this short piece of wire with the long telephone cable. Wire color is not important but connecting the same points is.

Dress the cable to the desired length. Solder one end of the new cable to the wires of the load cell. Remembering to feed the cable out through one of the holes in the base. I used the battery holder hole. You can use duct tape to make sure the wire does not touch the beams.

Step 6: Wiring of Display

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When I unsoldered the wires of the lbs/kg switch I found a nice blank place on the card for this switch to go. I had to drill the six small holes for the pins though. Even though the switch has six pins we only use two as an Single Pole Single Throw

Connect the outer end of the new cable to the display circuit card to match the wiring used at the load cell and follow the pix.

I didn't get fancy and just screwed the display on the workshop wall above the scale. Extra wire allows me to put the scale on the floor to.

Step 7: Not a Legal For Trade Scale, But....

Picture of Not a Legal For Trade Scale, But....
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A bathroom scale is not accurate enough for commerce, ie, when charging $ amount based on unit weight. All scales used as 'Legal for Trade' must be certified routinely to be remain legal.

But for parcel shipping or personal use, I think it is alright. In shipping the item is expected to be measured by the shipping company.

One of the first things I did was pre-weigh parcels before I went to the post office and was pleasantly surprised my results compared well to their results.

My goal was specifically the courier companies that pickup at my home repair shop. They somehow expect a person to guess what the weight will be for billing. I need to know how much the shipping charge is so I can pass the cost on to my customers. With the weight and dimentions I can get an estimate of charges on the interneet. I've never been billed extra after my shipments even when I underestimated weights lower than actual.

Step 8: There You Have It

Picture of There You Have It
Shipping Scale 9 Loaded.jpg
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Call over everyone you know, and even some you do not.

Plan your bragging plan while you await their arrival. Because unless they build one, they will never get one.

Enjoy

by
Egon Pavlis
Biomedtronix
www . Biomedtronix . ca
cool ! ....but omg that pisses me off that they sell scales for around 50$, after seeing theres like nothing in them :-|...
That strain gauge hardly constitutes "like nothing". They're pretty pricey, just small...like, for example, nice watches. Very precise, small parts mean expensive.
ya but i wouldent compair a watch to this, a watch is precise engineered little thing. and a scale is a easy made circut board with a few wires and a screen off of it
A strain gauge is a precise engineered part and it is the bulk of the cost for the scale. Like a lot of stuff if you break down the cost for what you actually get you are going to be angry, think about the cost to make a cup of coffee and how much people pay for it at any shop.
hello

so I am starting hacking the scale and here is what I got.

http://bit.ly/6ZELWs

I think it would work right?


arcticpenguin (author)  marcuantonio5 years ago

I'm pretty sure it will. Remember to be careful on dismanteling.  You need to know where every part goes if it all comes apart.  Good Luck.

Hi,  great hack,  do you know where could I find a scale so I can follow the instructable all I can find on ebay are the glass scales.

arcticpenguin (author)  marcuantonio5 years ago
Not sure where you are located in the world.  If you are in USA or Canada, try yard sales, junk stores, Value Village is good too. Try WalMart etc as well.
doppler136 years ago
I find a free and zero conversion solution to be even easier and more accurate.

1/ Weigh yourself on the scale
2/ Weigh yourself holding the package
3/ Subtract (Combined weight - your weight = package weight)
(repeat to confirm)

This ensures that the package is being weighed in the "accurate" end of the scale (most scales don't do well at the low end where many of the package weights are concentrated).
jumpfroggy6 years ago
This is such a great idea! Another good use: weighing baggage when you pack for an airplane flight. Getting it to just about 50 lbs is such a great thing, especially compared to getting to the ticket counter and realizing you need to move 4 lbs of stuff from one bag to another... right there at the desk.

Also, another good use: weighing someone who's disabled. I often want to weigh my wife, but can't because I'd have to hold her, then I can't see the scale. With this, I could weigh myself first, then weigh myself holding her, and the difference = her weight. Now I just have to find a scale that goes above 300 lbs so our combined weight doesn't overwhelm the thing (I'll be honest... it's my fault :) ).

Thanks!
scafool6 years ago
This is excellent.
nkrupp7 years ago
cool project. be aware, the presence of an outlet can cause error in the readings due to the longer wire length.
jmsanchez7 years ago
nice job :)
Prometheus7 years ago
For the purpose of calibration:

Penny (1990 [D]) = 2.5086g

Nickel (1999 [D]) = 4.9947g

Dime (1992 [D]) = 2.2634g

Quarter (1995 [D]) = 5.7065g

All values from the US Mint. Tolerances should be less than 0.01% for each unit (coin) "D" represents the Delaware mint. Can be found on the lower RH area near the bust portrait on the "heads" side of the coin. It's very small, but visible to the naked eye. "P" is the Philadelphia mint, and weights are not guaranteed to be equal.

Weights are given with a 0.1% tolerance of base numbers.....
static7 years ago
Hey man. People with big bellies would find this mod useful.
gtl66457 years ago
Great Project. I stumbled across some other mod on this site and having the attention span of a gnat, I immediately started browsing and found this project. I've struggled with the kitchen scale and the weigh-yourself-with-and-without technique and they left me wanting. I'm going to do this project as soon as I can, but I think I will put in an RJ45 jack at the display on the wall, so I can store the scale when I don't need it. Thanks for this!
Nice job. I agree, that would be good for estimating larger-package shipping weights. Your original conundrum reminds me of the confusion we had as kids when trying to weigh our pets on a bathroom scale - the scale seemed to not sense small-weight items (not to mention the frustration of trying to keep a wiggly cat or dog on a scale for more than a millisecond.) So we were very impressed when we saw the way our vet weighed pets - he stood on the scale holding the pet, then weighed himself again without the pet, and the difference equaled the weight of our pet. Ahhhha! Since then I have successfully used this method for weighing various items...pet or otherwise.
zphere7 years ago
Heh, that's pretty cool :) Did you happen to weigh some objects before and after the hack and compare the readings.. see if the result changed?
arcticpenguin (author)  zphere7 years ago
Yes, I have a block of steel I use as a rough tester. It's not really surprising because after all said and done all we are doing is placing a longer wire cable between the load cell and the display. The wire is thick enough that the resistance is still close to zero. The scale is not that sensitive to be affected.
randofo7 years ago
I don't mean to nitpick or give you a hard time, but most personal scales have labels on them telling you that they are not intended for commerce and shouldn't be used for this application... otherwise, well done. Nice hack.
arcticpenguin (author)  randofo7 years ago
I should have clarified the commercial use of scales a bit. I'll see if I can still edit it in. I did know that this is not accurate enough for commerce, ie, $ per lb, etc. These scales must be certified routinely to be legal. But for shipping I think it allright, as the item is expected to be further measured by shipping company. One of the first things I did was pre-weigh parcels before I went to the post office and was pleasantly surprised my results compared well to their results. My goal was specifically the courier companies that pickup at my home repair shop. They somehow expect a person to guess what the weight will be for billing. I need to know how much the shipping charge is so I can pass the cost on to my customers. With the weight and dimensions I can get an estimate of charges on the Internet. I've never been billed extra after my shipments even when I underestimated weights lower than actual. Thanks
Yeah, for shipping a couple of packages it should be fine. I just had that point beaten into my head while I worked in a shipping department some years back and against my better judgment felt compelled to share it.
arcticpenguin (author)  randofo7 years ago
I disagree that your comments should be "against your better judgement". I may know what I did to make the item and may even have some experience, but I am usually only privy to my own opinions and definitely like to hear from others. It's called my learning curve, and and after all is said isn't that why we are all here for.
I was going to reply with that exact information, now I see I don't have to. Good for, say, eBay estimations and whatnot.
LinuxH4x0r7 years ago
Cool! great for approximate estimations and shipping costs. Great job!
Awesome job. I've always wondered what the inside of those bathroom scales looked like. Wait up... these are the electronic ones! Noooooooooooooooo!

+1 rating.