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Integrating Helios Preisser distance gauge – one hour and done

Docklight to the rescue when the pressure is on

Recently we created a demo for the fullmo MovingCap position drives and a max GmbH linear axis. Such a toothed belt axis can feature excellent repeat accuracy, if designed and manufactured with great care. To showcase this, we had a Helios Preisser digital indicator with RS232 data interface at hand. Plus a small leaflet for documentation and close to zero time for the integration.

Helios Preisser distance measurement using fullmo Kickdrive and Docklight DLL
Helios Preisser distance measurement using fullmo Kickdrive and Docklight DLL

fullmo GmbH trade show booth with max GmbH axis demo
Ready for the show - rapid prototyping with Docklight and Kickdrive leaves you time to relax. 

The measurement gauge integration into our demo took me about an hour: Around 20 minutes of manual testing using Docklight and a standard RS232/USB adapter, and another 40 minutes for coding the integration into the actual demo UI. Docklight takes care of all the tricky parts here. The resulting demo was a Kickdrive UI Panel application. Kickdrive allows creating high quality HMI with smooth animations via the underlying Qt Quick / QML technology, but it also integrates the Docklight DLL API in a way that allows simple text messaging to do the interaction.

A Docklight project for the Helios Preisser protocol

The Helios Preisser products use a custom ASCII protocol with additional handshake logic:

  • RTS needs to be constantly high to supply Vcc for the data interface.
  • DTR is High by default, but needs to be reset to low for > 100ms to request a new measurement reading.
  • Communication parameters are slightly exotic : 4800 Baud, Even Parity, 7 Start Bits, 2 Stop Bits.
I defined a Docklight Send Sequence “Get” which looks like this in Decimal representation:
!!! 001 &&& 010 !!! 003

  • The first !!! Function Character with parameter 001 will set RTS=high, DTR=low.
  • &&& 010 inserts  a delay of  >= 100 ms.
  • !!! 003 will set RTS=highDTR= high.
Note: When opening the COM port, Docklight sets RTS=high, DTR=high by default.

Some quick manual testing:

05.10.2018 17:15:40.750 [TX] -
05.10.2018 17:15:40.952 [RX] -
05.10.2018 17:15:41.750 [TX] –
05.10.2018 17:15:41.951 [RX] -
05.10.2018 17:15:42.751 [TX] -
05.10.2018 17:15:42.952 [RX] -
05.10.2018 17:15:43.752 [TX] -
05.10.2018 17:15:43.954 [RX] -
05.10.2018 17:15:44.753 [TX] -
05.10.2018 17:15:44.955 [RX] -

Our gauge works – Great!

Now add a Receive Sequence to safely trigger on each reading.  We use ? wildcards for the variable measurement result, but anticipate the position of the decimal point. In ASCII representation, here is how this looks:
With Receive Sequence Comment definition:  Result: %_A(1, -2)
(Comment macros like %_A always come in handy.)

So our Docklight communication screen after receiving a new measurement looks like this:
17.10.2018 21:38:00.258 [RX] - +002.60<CR>

 Result: +002.60

Note: We later use the Result: string tag to easily filter out the actual reading using basic string processing.

Finally store everything as a Docklight project file helios_data.ptp .

The actual demo in Kickdrive / QML / Qt Quick

Now some quick integration into our QML / Qt Quick UI.
Note that what you see below is already a “bells & whistles” integration that deals with hot-plug / re-plug situations a.s.o. You know, trade show situations...

The added code in the QML / Qt Quick UI - everything is text messaging, so for the Docklight interaction we add:
       // Helios RS232 readout via Docklight
       property string sendDocklightCmd: "Docklight:KM_DOCKLIGHT:KS_REQUEST:"
       property string docklightReceiveToken: "KM_COMM_DATA:KS_INFO:Receive:Result: "
       property string docklightFail: "KM_DOCKLIGHT:KS_FAIL:"
       property bool docklightCommError: false
Two small convenience functions…
       function sendDocklightCommand(command)
             messageStrOut(sendDocklightCmd + command);
       function sendSequence(sequenceName)
             state = "CONNECTED"
             sendDocklightCommand("SendSequence(\"" + sequenceName + "\")");
You have to love timers in Qt Quick….
       Timer {
             id: demoSensorReadout
             interval: docklightCommError ? 3000 : 200
             repeat: true
             running: false
             onTriggered: {
       Timer {
             id: demoSensorTimeout
             interval: 4000
             repeat: false
             onTriggered: {

Here is the main function that processes all incoming messages, be it CANopen or the Docklight API command results. ….

       function processMessageStrIn(msgStrIn)
Note that loading our tried and tested Docklight project “helios_data.ptp” avoids any possible headache.
             // First message - this arrives once the project is loaded
             if (msgStrIn.indexOf("KM_APPLICATION_CONTROL:KS_INFO:projectloaded") !== -1) {
                    // Docklight project load
                    // tell Kickdrive to forward any Docklight communication output                          sendKickMessageOut("Docklight:KM_SETPROPERTY:KS_REQUEST:CommProcessingMode=AR");

             else if (msgStrIn.indexOf(docklightReceiveToken) !== -1) {
                    // watch out for the Result: tag we defined in our Receive Comment
                    docklightCommError = false
                    var strAnswer = msgStrIn.substring(msgStrIn.indexOf(docklightReceiveToken) + docklightReceiveToken.length);
                    // skip one leading zero
                    demoMeasurementValue = strAnswer.substring(0, 1) + strAnswer.substring(2);
             else if (msgStrIn.indexOf(docklightFail) !== -1) {
                    docklightCommError = true

The graphical widget for the gauge simply applies the demoMeasurementValue property value:

       GaugeDisplay {
             id: measure2
             value: main.demoMeasurementValue
             x: 846
             y: 518
             scale: 0.35
             isometric: true

Again - you just have to love Qt Quick for how easy this can be bolted together.

The resulting demo ran smoothly throughout the trade show days at MOTEK 2018 and SPS 2018. It’s why we made and use Docklight – we need something that “just works”.

Docklight and Kickdrive running demo SPS IPC Drives 2018
"Just works" software built with Docklight and Kickdrive - no glitches, no hiccups, no freezes, no restarts. 

So if you have a similar task / project and need some pointers – let us know. For Company License and Docklight DLL license customers we also provide in-depth application specific support, including example projects and scripts to get things started. 

Marco Flachmann and Oliver Heggelbacher
- The Docklight Developers –