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  • Author Author: phoenixcomm
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NexGen: Fuel Indicator: Testing The Display

phoenixcomm

imageThis picture on the left is just to remind you all of what I am trying to get working.  Each HDSP-2131 display has 24 pins that give you 48 pins to deal with. Now let us complicate the issue the pins come out on a 30-pin connector of which 4 are for power and ground. So now I have 28 pins for the interface.image

Other people have used similar displays ie  Wise Time with Arduino and others. Most implementations I have seen use a Flip-Flop to load the characters, but why go to that solution? The Arduino Mega 256  has only 54 digital GPIO pins. My pin count is higher as  I needed 20 pins +  8 Data  = 28 pins + 5 pins for my switches (reduced to 3-bit BCD and one interrupt pin), CAN module on pins 53, 52, 51, 50,  and the USB driver and interrupts.  This makes my head hurt! image

So I freed up my 8-bit Data-Ports pins by using an 8-bit I2C port expander which is mounted on the same  PCB that holds the 30-pin header that the display plugs into.

 

image

My biggest problem is that the CAN libraries (Arduino) are Master-Slave.
But CANbus is democratic which means any node can become the Master.
  And this is where the problem lies.

I still don't have a clue where to mount my Arduino Mega. image  My CAN bus modules output will be routed to a USB-A  or an RJ45F connector.

So to speed up testing before  I use my jumpers.  The only pins I will be Wire-Wrap will be the Data Port to the display header.

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  • It's a lot of hardware and a lot of pins to deal with. Is your goal to stick with the original technology?

    I see you lower the count by using the expander.

    Maybe we can work together here to create a design that uses the same display but avoid that the microcontroller needs to drive that many individual I/Os.

    CAN alone should be enough to tell the display what to do. The rest could be added to the display unit by adding a single CAN-aware microcontroller close to the display ...

  • in reply to Jan Cumps

      In CAN aerospace there is a lot going on the CAN bus itself.

    First, you have to deal with the "heartbeat" (node 0), this happens every so often each node responds with its status good, bad, or whatever.  What heartbeat does it let you do is to add or removes nodes at will. Without a power down.

    Two, you have to deal with receiving a query for this node, as this node can respond to over eight addresses. this is normally handled by filtering.

    Three, you have to deal with its switches, and outbound messages.

    This would be to FILL tank number 4.

    First, you would have to move the up/down  switch appropriately till the lower display indicated #4

    Second, you will receive 20 from the host

    Third, you will receive  tank 4 max = 30

    Forth, the lower display now indicates #4 20 - 30

    Fifth, You now raise FILL sending a message to the host.

    Sixth, the lower display now displys, #4 - 30G

    Seventh, The upper display will display the weight (load) of fuel in tank #4

     

    also take al look at the spec. https://www.stockflightsystems.com/tl_files/downloads/canaerospace/canas_17.pdf

    one of the cool things most nodes they have  the parameter name, Suggested Data Type,  Units, Note;

    if you look up nodes 668-675 (34.57), Fuel Tank # quantity, FLOAT SHORT2, kg but here kg is, not appropriate as fuel is pumped in US Gallons.  This is the job of the crew chief to do the conversion for weight and balance.   Car and AVi Gas both come in at 6.36 pounds per gallons. So my weight in tank #4 with 20 USG is 127.2 pounds or × 0.45359237 = 57.696949464 kg

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  • in reply to Jan Cumps

      In CAN aerospace there is a lot going on the CAN bus itself.

    First, you have to deal with the "heartbeat" (node 0), this happens every so often each node responds with its status good, bad, or whatever.  What heartbeat does it let you do is to add or removes nodes at will. Without a power down.

    Two, you have to deal with receiving a query for this node, as this node can respond to over eight addresses. this is normally handled by filtering.

    Three, you have to deal with its switches, and outbound messages.

    This would be to FILL tank number 4.

    First, you would have to move the up/down  switch appropriately till the lower display indicated #4

    Second, you will receive 20 from the host

    Third, you will receive  tank 4 max = 30

    Forth, the lower display now indicates #4 20 - 30

    Fifth, You now raise FILL sending a message to the host.

    Sixth, the lower display now displys, #4 - 30G

    Seventh, The upper display will display the weight (load) of fuel in tank #4

     

    also take al look at the spec. https://www.stockflightsystems.com/tl_files/downloads/canaerospace/canas_17.pdf

    one of the cool things most nodes they have  the parameter name, Suggested Data Type,  Units, Note;

    if you look up nodes 668-675 (34.57), Fuel Tank # quantity, FLOAT SHORT2, kg but here kg is, not appropriate as fuel is pumped in US Gallons.  This is the job of the crew chief to do the conversion for weight and balance.   Car and AVi Gas both come in at 6.36 pounds per gallons. So my weight in tank #4 with 20 USG is 127.2 pounds or × 0.45359237 = 57.696949464 kg

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