Introducing the New DYI DRO Adapter Kit

Thursday, March 5, 2020

From the start, my goal for TouchDRO was to create a do-it-yourself DRO project that would allow people to build a powerful digital readout as inexpensively as possible. To make the project more accessible to people who are not comfortable with electronics, a few years ago I started offering pre-assembled adapter boards for sale.

Since the boards are manufactured in the USA on a relatively small scale, their cost is much higher compared to a scratch-built DIY DRO adapter. The original TouchDRO Mixed Scale DIY Kit was designed to bridge the gap at a price point that was about half-way in between. The kit was very successful from the sales standpoint but created an unexpectedly large support burden.

Because I wasn't able to sustainable deal with it, I pulled the plug on the kit and removed it from the store. Since then, I've been getting a constant trickle of emails asking when the kit will be available or if I have any left for sale. After some "soul searching" I decided to offer a new version of the TouchDRO DIY kit, taking into account lessons learned from the last one.

Overview

As the name suggests, this is a kit of parts needed to build a TouchDRO scale adapter. It includes a bare printed circuit board, preprogrammed MSP430 microcontroller, and the rest of the parts needed to complete the circuit. Functionally, the new DIY DRO kit is very similar to the TouchDRO Adapter for iGaging scales and TouchDRO Adapter for Shahe scales. In fact, it uses the same firmware version and the circuit that is almost identical. As a result, it supports all of the scales that the other two adapters support:

The new TouchDRO kit's design is based on the adapter for iGaging scales but has a few minor tweaks. First and foremost, the kit is set up to easily allow using a battery pack to power the scales. The battery pack can be connected to provide a backup power source when the main power supply is disconnected. Alternatively, with omission of one diode, the scales can be always powered from the battery pack. Second difference is the use of a dedicated power LED in addition to the heartbeat LED that is used by the pre-assembled boards. On the other hand, there is no BlueTooth LED on the board since that is available on the HC-05 module. Finally, the board has broken out UART Rx and Tx pins, so it can be easily connected to an external UART-to-USB adapter.

The kit uses high quality name-brand parts and immersion Gold plated PCB that is assembled to IPC-A-600 Class 2 standard and 100% electrically tested by the manufacturer. To maximize the noise resistance, the kit includes dedicated bypass capacitors for each axis, carefully routed traces, and double-sided copper pour stitched with vias to provide continuous ground plane. Furthermore, all capacitors and resistors are considerably underrated for extended life and reliability. The result is an easy-to-assemble DRO kit that costs only slightly more than a scratch-built one but offers excellent noise resistance and long-term reliability on par with the pre-assembled boards.

New TouchDRO Kit vs. Old Mixed Scale Kit

This TouchDRO kit is not intended as a direct replacement or an upgrade of the old TouchDRO Mixed Scale kit. The latter was designed to work with all supported types of capacitive scales, including the legacy Chinese 1.5V scales and inexpensive digital calipers. Its purpose was to allow people to use legacy 1.5V Chinese linear scales and cheap Chinese digital calipers. In practice, the vast majority of people bought the kit to be used with iGaging scales, since it was much less expensive than the pre-assembled board. This caused a few problems.

First and foremost, interfacing 1.5V scales to 3.3V MSP430 necessitated a signal amplification circuit, which made the kit much more complicated than the basic iGaging adapter. Second, TouchDRO Mixed Scale firmware is not optimized for iGaging EZ-View and other 21-bit scales. Finally, the comparator circuit was not ideal for the iGaging scales, which need a very specific input stage configuration to work reliably. Combined with the fact that a lot of people who bought the kit had very limited electronic assembly experience, didn't follow build instructions, forgot to configure pull-up/pull-down jumpers - all this led to a number of issues with reliability.

New TouchDRO DIY Kit vs. Old Mixed Scale Kit

In contrast, the new kit is optimized specifically for the iGaging EZ-View DRO, iGaging Absolute DRO Plus and the new Shahe scales and does not support 1.5V scales. It uses the same version of the firmware that has been shipping on the pre-assembled iGaging and Shahe scale boards for over a year with an excellent track record. The new circuit is much less complex; so, the assembly process will be much more straightforward. That said, it provides a bit of flexibility for "hacking": all through-hole header pins are laid out on a 0.1" grid, and power input pins are broken out to a 2-pin header; so, the whole board can be plugged into a breadboard.

Price and Availability

At the time of this writing, I have 50 kits ready to ship and [almost] enough parts for another 200. The only holdup as far as the parts go are the BlueTooth modules. There is no HC-05 equivalent module offered from a US-based manufacturer, so I have to order them from China. Between the Chinese New Year and the Coronavirus outbreak my order has been delayed for more than a month. That said, I expect to have the kit listed for sale no later than March 23rd. The price will be $48, which includes free domestic shipping; international shipping will cost extra.

Summary

I was a bit apprehensive about offering a DIY kit again, given how much support overhead the original Mixed Scale kit created. That said, I realize that a pre-assembled adapter is relatively expensive and many hobby machinists aren't comfortable with scratch-building a DIY DRO adapter.

The new kit is much less complex, it provides a great option for people who have very basic soldering skills and want to build a DRO on a budget. While the kit is indeed much less expensive than a pre-assembled board, it uses high quality PCB and name-brand components, and if built correctly, will provide excellent long-term rel iability.

7 comments :

  1. is it possible to buy this kit without the HC-05? I have one leftover from an earlier project.

    Bill

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  2. Hello Yuri, when do you think you will gives us a new software which will include The Chinese linear glasses?
    My diy board is waiting this 😉. You have said one year ago that you will prepare a new version for download
    Thanks

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    Replies
    1. https://files.yuriystoys.com/msp430/DigitalReadout_iGaging_2.00.txt

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  3. Thank you Yuri, one more question please. I have done a diy mixed board... can I use the DigitalReadout_iGaging_2.0 firmware on it if I configure correctly the jumps?
    thanks

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  4. In theory it should work, but I haven't tried it.

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  5. Thank You very much for your support.

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  6. Hi Yuri - I've built one of the new DYI DRO boards - and all seems to be well with the exception i'm getting only 0000 on the display. I'm using a USB breakout board and have double checked the wiring back into the gauge - all check correctly as does the +ve on the gauge.. The gauge reads ok on its own display. The gauge I'm using is a new igaging DRO Pro - is it possible they have changed the firmware on these?

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