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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

  • in reply to michaelkellett

    I think your pin math is way off you say I only need 15 pins ouch! Data = 8pins,  Address = 5 pins, Control = 7 pins so that's 20 pins!  I don't want to make a new PCB for the display. You should understand part of my mantra: please read NexGen: Audio Panels Ins and Outs I am using the original display PCB. If I try and remove the display and screw it up, I'm out $150.00, so removing and rebuilding the display PCB is a non-starter. 

  • in reply to phoenixcomm

    I missed the address pins, still the basic idea holds, the suggestion was not that you remove the display chips from their boards but make a board that would plug into the exisitng display board. But the only picture I have to work on is the one with you holding the board in your hand.

     

    MK

  • in reply to michaelkellett

    Take a look at this: NexGen: Hacking the Fuel Load Indicator. This shows more pics. There is nothing worth mentioning on the reverse of the display board.  just some caps, and the connector to the secondary board which held an MC68HC11 8 Bit Microprocessor but if you try and read it. It self destructs. image

  • in reply to phoenixcomm

    Well, I'm not sure what you want to do with this but you could easily (ish) replace the old controller board with you own, it would interface to the display board the same way as the old one. It might be nicer to make the old controller board work again but that doesn't seem to be an option.

     

    MK

  • in reply to michaelkellett

    What I want to do is to use the original Display board and I made a control board out of vector board. The only thing that board will hold is the female header with long tails and an MCP23017 in a Wire-Wrap connected on the bottom this is protruding on top as well as the header pins. The expander has two 8 bit ports, which can be used separately. So I can use port -A for the addresses bus A0 - A4 and I can use port-B for the databus D0  -D7.

    I was going to use the TI  PCF8575 but I can not configure this as two (2)  separate ports.

    ~~Cris

    PS I will connect this to an Arduino Mega.

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  • in reply to michaelkellett

    What I want to do is to use the original Display board and I made a control board out of vector board. The only thing that board will hold is the female header with long tails and an MCP23017 in a Wire-Wrap connected on the bottom this is protruding on top as well as the header pins. The expander has two 8 bit ports, which can be used separately. So I can use port -A for the addresses bus A0 - A4 and I can use port-B for the databus D0  -D7.

    I was going to use the TI  PCF8575 but I can not configure this as two (2)  separate ports.

    ~~Cris

    PS I will connect this to an Arduino Mega.

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