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Using The DRO

Front Panel
The front panel of the DRO should look something like that given below. The LCD display is sited behind the transparency on the left, and the 21 tact-switch actuators are sited underneath their individual red pads.

DRO Front Panel

The keypad logos are hopefully self-explanatory, but briefly consist of:

Numeric keys 0-9, together with decimal-point.
The axis [...]

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DRO – Tools You Will Need

Board Assembly
The following should be considered essential for mounting the components on the circuit boards, and attaching pin-headers to the LCD display:

A soldering Iron – 15-25 watts, preferably with a choice of 2 bits – one conical, the other flat (see photo)
Solder – I use 22swg resin-cored 60/40 tin/lead alloy (Rapid Electronics)
Solder braid (’Soldamop’ from [...]

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DRO Bill of Materials – 2

Switches S1-S21. These are miniature TACT switches for the keypad and it is essential to purchase a similar product to that used in the prototype otherwise use of the keypad PCB may not be possible.
The switches used have the following characteristics according to my Eagle schematic editor: The original manufacturer is Omron, and the ‘package’ [...]

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DRO Bill of Materials – 1

You will need the following items. The photographs are for the benefit of those new to electronics, also I’ve included a link to a datasheet where possible, to satisfy the curious. So I ask the patience of those to whom all of the following is old-hat!


Main processor printed circuit board.(DRO V2.1)

DRO Printed Circuit Board [...]

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DRO Component Identification

Component Identification
If you are already fully familiar with electronic components, then feel free to skip this section, as it’s mainly intended for those who have none or little experience of electronics. Components are also illustrated in the DRO Bill Of Materials page.


Resistor Symbol

Resistors are usually cylindrical in shape with axial wires emerging from each [...]

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DRO Main Circuit


If you have followed the Design Walkthrough, we have now covered almost everything in the DRO design, apart from the liberal smattering of decoupling capacitors. (all of value 100nF) Apologies for the rather busy circuit, and if you need to look closer, I advise downloading the (free) evaluation of Eagle and viewing the schematic in [...]

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DRO Design Walkthrough

A WalkThrough The Design
Foreword: You don’t need to read any or all of this to build the DRO, but I hope you will be tempted. It’s included for those who are interested in the analysis and design required for what is a moderately complex piece of electronics. Please note that in the following sub-circuits, the [...]