Fitting a microhard on the Bixler

So I'm currently trying to fit a microhard n920 onto a Bixler, and unfortunately I don't see a way to do this without also having the dev board (doesn't look like they have a small breakout board I can wire up to).  I've managed to get it to fit into the fuselage, but don't see a way to connect the RS232 to the TTL converter. Anyone have a solution or know of some RS232 angle adapter that might work?  Alternatively, is there a way to wire this using the RS485/422 pins?


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              • Hallo Jaron,

                the board I designed has been manifactured already. I can certify it as working since I'm actually using it in our prototypes... for your use I will provide a simplified version since there are a number of features that are useless.

                I will be off holiday January the 7th.

                Best Regards,


                • Mike,

                  Thanks that looks pretty good! Compact for having a 232 port. I wanted to share with you thoughts that I had about the design when I was thinking about it in January. My jury is our on the 232 connector, probably would like one without it for smaller aircraft and one with it for larger aircraft. I was originally just anticipating setting and forgetting the programming, however things can always change and then it might be a pain to de-solder and stick back on a programming dock. If you wouldn't mind please take a look at my notes on the attached pdf and let me know how far off your design is from my vision.

                  Thanks again, 

                  Jaron Denson

                  Microhard Modem Breakout Board.pdf

                  • Hallo Jaron,

                    RS232 is an interface standard the use of DB9 connector is a common practice but it's not mandatory unless you want to use a standard RS232 cable (that typically uses DB9 connectors) to interface to the between DCE and DTE.

                    Connecting the same UART port to two different paths one of which left dangling is nor a good idea. I would suggest a different approach: the design of a board that should interface n920 with two different autopilots (with incompatible I/O levels) can be solved using a single connector solution and a dual supply level translator like SN74LVC1T45. I would not mind about size and type of the connector because in any case you will need an interfacing cable so why not use the best connector solution saving space a matching n920 power requerements? Check for HARWIN GECKO serie...

                    I would anyway leave a path with a RS232 level translator and a separate connector (and a custom cable) to allow configuration/operatiion of the modem without need to reflow. Of course if you're going to operate the board trough a legacy free I/O laptop you may also consider to put an USB interface instead RS232.

                    Fitting the whole circuit inside a small footprint like you request would lead to put power management units quite near the modem unit. Without a proper grounding (and maybe an extra ground plane) this would leave a path open to noise coming from regulator... you'll probably need a 4 layer board. 

                    If the size is your biggest issue please consider also P400/P900 microhard units.. the desing is a little ore challening but the benefit in size / weight could pay the the effort.

                    If you need help please don't esitate to ask I'll always appreciate a challenging design.

                    Best Regards,


                • Mike,

                  That's great news that it is a working prototype, I am super excited now, its like Christmas all over again. Few more questions for you ( I know you are on vacation so feel free to ignore until you get back).

                  1)How is the power supply to the modem handled? Is there a voltage regulator on the board or do I have to bring in my own clean 3.3V? According to microhard data sheets the modem can draw 1.5A at 1W Transmission power, I plan on transmitting at 1W so I am trying to figure out my path based on what you have done.

                  2) How did you handle the external connections coming into the board? Solder pads/Thru Holes/ Plug?

                  3) I saw that you put a logic level converter on it in a previous post. For my own understanding why is this necessary if the ARDU and Pixhawk pinouts states Rx and Tx signals at 3.3V? I thought that a logic level converter just switches the signals bidirectionally from 3.3v to 5v, was this just to future proof it or allow other devices to be used with it?



                  • Hallo Jaron,

                    this's the simplified version of the interface board.

                    If you need a more compatc one without the RS232 level translator just ask I can update the design ASAP.

                    Also if you have a very narrow place to fit this in we can exchange the DB9 connector with a smaller one even if this may be render the whole thing uncomfortable when programming the modem trough a PC (of course you can arrange a custom pc interface cable..



                    n920 IF Board.pdf

                    n920 IF


                  • Hallo Jaron,

                    1) I'm using the same switching regulator Microhard uses on their boards.
                    The Vin range it's 9-36 volts (or maybe 9-18volts) so you can provide a
                    supply by battery or other non regulated sources.
                    2) trough-hole connectors (1.27 or 2.54mm pitch). If you need I can arrange
                    a different connection anyway.
                    3) the logic-level converter is for RS232 to LV-TTL conversion of course if
                    you need just the raw signals from the modem I can drive them to the
                    interface connector.

                    Best Regards,
                     Michele Santucci

    • hi, I am divya jetty engineering student, working on the wireless communication for long distance. I am using the n2420 which is similar to n920 form microhard company. I was able to interface the module with the other controller using RS485. but know i want to use the module without the mother board. please anybody help me out. I am not able to find any connector for 60 pin which was described before. And @ Mr.Miclhele Santucci can u please help me in designing. 3702523660?profile=original

      • Hallo Divya,

        what do you mean with .. "I'm not able to find any connector for 60 pin..." you mean that you're unable to identify the product or to find a reseller?

        Anyway the connector part I'm using (and that you can use as well) is a Kyocera 24-5046-060-600-829+ you can find it on Mouser (code 581-245046060600829+), you should find a reference also in the hardware integration manual of the microhard modem.

        About design support... if you are using KiCAD I can provide you the footprint of the connector as also 3d models. If you need more infos or help in e-design please don't esistate to ask (but be a little more specific in your questions).

        Best Regards,


        • Hi Michele Santucci,

          I guess i am back on conversation after very long time (Please don't mind). As I said before, I want to use only daughter board for my project. I came across the conversation in the blog, of working prototype. May i know more about it. I feel this may help me in the project. Please do the need full.

          Thank You

          Divya Jetty

        • Thank Michele Santucci for your response. I mean to say that i am not able to interface the daughter board alone with any controller. Can you just help me how to interface 60 pin daughter board to any micro-controller. I am struck there.

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