DRO for Harbor Freight 47158 based on Harbor Freight 93293 Calipers

[Temtu]

Greetings,

I want to add very inexpensive triple axis remote mounted DRO to Harbor Freight 47158 using Harbor Freight 93293 digital calipers.

I will make the electrical design + PCB layout + Electrical Testing. I need small team of enthusiast to brainstorm to find the best method to mount the caliplers to the axes and make the mechanical prototype.

This is a non-profit activity. Everybody involved, including the forum will get pictures, drawings and part list.. Then it is upto individuals to implement the working solution themselves.

I do not have plans to sell this jointly developed solution.

I ask collective mechanical help from interested parties.

Max,
Plantation, FL

PS: Idea is to connect small piggy-board to caliper body and convert LCD signals to serial using triple 74HC165 and then transmit using 6 core, flat, oil-resistant PVC jacketed cable to triple 74HC595 to convert back to parallel and drive the remote mounted LCD dismounted from the caliper. I envisage that triple LCD, (one for each axis) will be mounted under a Lite Source LSM-195 gooseneck magnifier lamp so that user can see LCD's as well as the work-piece behind the magnifier lens simultanoeusly.

PPS: I do not want to re-invent the wheel. If anybody knows similar triple axis conversion under $ 75 material cost ( $25 lamp + $25 three Calipers + $25 Electronics) please advice.

[darkith]

There's a DRO kit available for digital scales/calipers, the schematics/code are free for personal use, but you'd have to purchase the PCB or design your own.
http://www.shumatech.com/products/dro-350/index.htm
The Bill of materials for the kit suggest a price of $110 USD for the DRO part, not including the scales/calipers.

They also publish the protocols for the digital scales/calipers which have a connector, so you wouldn't need to read the LCD signals (ugh).
http://www.shumatech.com/support/chinese_scales.htm

If you wanted to go cheaper, it wouldn't be that hard to read the digital signals into a PIC or something, and then output the info to a serial LCD...that might save a bit on component/PCB cost as opposed to the parallel driven LEDs, but the contrast would be lower.

D.

[Temtu]

Hi Darkith.

Thank you for the info..

I did check the shumatech... Here I am looking for under $50 solution, including the triple calipers, the display electronics, cables, PCB's, connectors but exluding a nice gooseneck magnified lamp.

Besidem 47168 is a micromill and I could not find tailor-made DRO for this unit..

Any advice ?

M

[Stepper Monkey]

The digital signals are actually coming from those calipers are non-standard. I have the pinouts and protocols somewhere but they are actually pretty bizarre. I'll see if I can't find and post them.
I did see someone make a converter to change the signals over to a standard format for input into more standard DRO head units.

[Temtu]

Hi Stepper,

Very nice of you to respond.

To keep the cost down, I do not plan to translate the signals coming from the caliper.. I plan to use same LCD glass used by caliper but glass shall be mounted to end of long 6 core wire. Then you can place the glass where ever you like.

No need to mention that thes lines shall be properly buffered and glass will be inside a protective shell, mounted under the same magnifying lamp where one can see the DRO and object same time without large eye or head movement.

Max

[sansbury]

That's an interesting approach. I would be a bit concerned about the ease of breaking something important when disassembling the caliper. I like the idea of using the calipers though because they cost a lot less than the scales.

One approach to consider would be the use of something like the Arduino control board. These can be had for about $30 and provide a full microcontroller with serial I/O, PWM, and interrupts. This would make it easy to interface to an external display (which could be bought cheaply too) and also make it easy to expand the DRO to provide functions like patterns and offsets.

[Temtu]

Dear Friends,

I already disassembled the caliper. There nothing to break.

All I need is somebody fix the mechanical issues. I will address the electrical details.

I suggest to place the LCD glasses right under the illuminated magnifying lamp so that all triple LCD's and the work piece is both illuminated and enlarged.

What do you think ?

M

[xiphmont]

Originally Posted by Temtu Dear Friends, I already disassembled the caliper. There nothing to break. All I need is somebody fix the mechanical issues. I will address the electrical details. I suggest to place the LCD glasses right under the illuminated magnifying lamp so that all triple LCD's and the work piece is both illuminated and enlarged. What do you think ? M

...I'm wondering how you plan to attach wires to the sintered contacts of the glass LCD... you can't exactly solder them on.

[Temtu]

Originally Posted by xiphmont ...I'm wondering how you plan to attach wires to the sintered contacts of the glass LCD... you can't exactly solder them on.

I will use the Zebra strips which come with caliper.. No soldering to LCD glass.

Below is very brief description of my idea.

--Buy 3 calipers. Dismount the LCD glass + Zebra. Mount newly made small PCB with necesary electronics where the LCD glass was.

--Add flat flexible cable + wire strain relief to calipers.

--Cut/drill and mount the claipers to the three axes of the mini-mill

--Buy gooseneck magnifiying lamp and mount to the Mini-mill.

--Make newly machined plastic LCD housing which fits exactly under the manifying lamp. One for each axis )

--Mount the LCD's with newly made PCB + cables from calipers with necesary electronics under the magnifying lamp (=to the magnifying lamp)

--Adjust goosneck of magnifying lamp to see part & LCD's same time.Vola.

In doubt, please ask.

PS: I will make all the PCB's + electronics using P->S and S->P CMOS IC's..

[darkith]

I've seen a fair number of different ways of mounting calipers to mills...there are some generic solutions, and some solutions which are specific to mill particulars (e.g. depends if you have extended tables/leadscrews, mounted to custom limit switch blocks, etc). Lots of examples if you search for "dro calipers". Insulating the body of the caliper to prevent grounding issues appears to be the most common detail.

I'd be curious if the circuitry side is feasible. I dunno what the LCD signals are like, but if you're converting parallel to serial and back, I'd wonder about syncing the conversion to the LCD update from the caliper electronics, syncing the clock across the two convertors, bandwidth, clock rates/skew, crosstalk, etc. Haven't done any P->S->P work myself, so I'm just theorizing...tricky without a block diagram or details, so I might be barking up the wrong tree.

Temtu, have you prototyped/breadboarded the electronics to make sure they'll work over a long enough cable yet? I'd start there before refining the mounting...that's comparatively easy I think.

D.

[Temtu]

Originally Posted by darkith I've seen a fair number of different ways of mounting calipers to mills...there are some generic solutions, and some solutions which are specific to mill particulars (e.g. depends if you have extended tables/leadscrews, mounted to custom limit switch blocks, etc). Lots of examples if you search for "dro calipers". Insulating the body of the caliper to prevent grounding issues appears to be the most common detail. I'd be curious if the circuitry side is feasible. I dunno what the LCD signals are like, but if you're converting parallel to serial and back, I'd wonder about syncing the conversion to the LCD update from the caliper electronics, syncing the clock across the two convertors, bandwidth, clock rates/skew, crosstalk, etc. Haven't done any P->S->P work myself, so I'm just theorizing...tricky without a block diagram or details, so I might be barking up the wrong tree. Temtu, have you prototyped/breadboarded the electronics to make sure they'll work over a long enough cable yet? I'd start there before refining the mounting...that's comparatively easy I think. D.

Everything which is not tested, does not work. So in one hand you are right that P->S and S->P it might be challenging... However, is chicken or egg first ? To me, unless I find somebody with precission milling experinece to mill the Triple or Dual LCD housing with thin Zebra holder, this low cost idea is just an idea. I learn every day and have been part of teams ( or alone) shipped electronic products for many years, for many hundered millions...

This low cost idea could be another learning experience ))

PS: Harbor freight 93293 calipers are reinforced plastic so grounding is not an issue.

[darkith]

Nod, your original question was related to "mount the caliplers to the axes and make the mechanical prototype", so I thought that's where the hangup was. Milling a precise fit for the LCD, PCB, and zebra strip could also be challenging.

My point was to start on the harder parts of the problem to ensure that they're solvable before progressing to the simpler parts. As it stands now, I'd try crafting a simple 1 LCD temporary holder for the LCD, PCB, and zebra strip. Then try connecting over very short wires for testing. Once that's working, I'd build the P->S->P circuit and test it over short wires. If that works I'd test it over long wires. If that all works, you're at the point of looking for a final mounting solution for your LCDs and calipers.

Anyways, I am interested to see how you make out. If I ever get around to building my cheap DRO using serial LCDs instead of more expensive LEDs, I'll share it. I'm still debating if I'll build it though, as I might just go straight to CNC and skip DRO.

D.

PS. I have one of those plastic calipers....got it at the canadian equivalent of HF. I'll point out that the accuracy printed on the back is only .01" (HF's listing is wrong), and even if you trust that, it's not very accurate for a lot of work. I bought mine and pretty much gave up on it...the cheap metal calipers for $15 are a much better deal IMHO.