[DCS-BIOS] Public breakout board design?

Has anyone released some MAX-487 based DCS-BIOS break out boards? I have a design about 75% ready for first prototype, but was away from my project for the better part of a year. (Life!)

I need to modify my boards from MAX-485 to 487, and then I'll get ready to pull the trigger on some prototypes.

I'd like to see a suggested PCB design for those MAX487 too

I'd look at some TI RS-485 transcievers. The MAX chips are 3 times more expensive which will add up over an entire pit.

I'd look at some TI RS-485 transcievers. The MAX chips are 3 times more expensive which will add up over an entire pit.

I just received my eBay order for 20 additional MAX487 chips at a cost of $6.00 US. I wouldn't consider that expensive.

Normal channel pricing on the MAX487 chips are significantly higher than that. The lowest listed price for a MAX chip at quantity of 1000+ is $1.63. Based on that pricing, plus the fact that there at least three different sets of markings on the chips pictured in the current ebay listings. I'd consider those chips a high probability of being counterfeit, meaning they may or may not match the specifications on the datasheet. That being said, lets talk about the reasons to select an RS-485 chip. There are four main differences between these chips power draw, data rate, bus load and price.

Data Rate

For our purposes we want the highest data rate we can sustain. We will be round robin asking boards if they have inputs so we want this as fast as possible so the latency is low between a switch being flipped and the switch acting in game. Ideally this is 250ms or less in order to "feel" right and not delayed. For DCS-BIOS which is mainly centered around an arduino echo system the majority chips (ATMEGA328P or ATMEGA32U4) can only sustain 250kbps before we start having problems keeping up. Faster can probably be attained by dropping the arduino libraries but that defeats some of the purpose of allowing folks to work in an easy environment. Some arduino compatible boards like the teensy series are able to go faster, but many of them are 3.3v not 5v. Be careful when using one of these as many of the RS-485 driver chips are 5v.

In regards to RS-485 chip selection make sure the chip you select has a high enough max rate to enable your desired speed. I prefer to have my chip rated higher than my desired speed. For me that eliminates the MAX487 chip as it's max is 250kbps, so I would move to the MAX485 or MAX1487 chips with 2.5Mbps if you want to stick witht he MAX lineup.

Bus Load

The RS-485 standard specifies a max of 32 devices on a single bus. This is not an arbitrary number that can be played with. There is a lot of math and engineering around the electrical characteristics that these drivers are designed around. That being said as technology has gotten better chip manufacturers have started designing "partial load" transceivers where they have half or quarter of the electrical load on the bus, increasing the number of devices on the bus.

For our use case we really will never have more than 32 devices on the bus. As I said above you want the latency of sending switch information at 250ms or under which means you need to poll each board 4-5 times per second. At 250kpbs you don't have enough bandwidth to send 30fps updates from DCS BIOS and poll more than a dozen or so panels. This means quarter load transmitters are not a value add for us, so don't pay more for them.

Power Draw

Chips can have radically different power draw and you need to do the math in terms of total power draw for your entire pit not just a single card. When calculating total power draw keep in mind there is only one transmitter at a time per bus, but everyone else is receiving. Calculating actual supply draw is a little more complicated, but the draw values in the table below will give you directional comparison between the chips.

Some chips have a lower power shutdown (ex: MAX481) where you can shutdown and draw even less current. Since we never have an situation where we want micro-controller on but RS-485 off the extra feature is useless to us. In addition we are usually trying to max out the number of IO lines to our inputs so we don't want to dedicate another IO pin to control power mode of the transceiver.

Chip Comparisons

Here is a quick list of chips that I found which are pin compatible when using DIP or SOIC variants. I have only included chips which have higher than 250kbps as max data rate, and eliminated variants that only have features that don't matter to us. These are all 5V chips, 3.3V variants all cost $2.80+.

[TABLE]Mfr|Chip|Cost|Total Cost|Max Data Rate (Mbps)|Receiving (mA)|Transmitting (mA)

MAXIM|MAX485|$1.68|$84.00|2.5|0.3|0.5

MAXIM|MAX1487|$1.68|$84.00|2.4|0.23|0.3

Texas Instruments|SN75176|$0.68|$34.00|10|26|42

Texas Instruments|SN65HVD485E|$1.72|$86.00|10|1|2

Exar|SP485|$0.78|$39.00|5|0.9|0.9

Exar|SP485E|$0.78|$39.00|10|0.6|0.9

ST|ST485C|$0.76|$38.00|2.5|0.5|0.9

ST|ST485E|$0.79|$39.50|5|0.3|0.4

Intersil|ISL81487E|$1.34|$67.00|5|0.35|0.4[/TABLE]

All pricing is for 50 chips from Digi-Key for an SOIC-8 chip, but I checked several reputable distributors and they are all pretty close. Through hole DIP versions are a little higher across the board.

The TI chip I was refering to was the SN75176, which has obviously more power draw but significantly lower cost. It had been a while since I did a comparison and I will probably use the ST485C for my panels control boards.

Thanks for the info, Gadroc. Great comparison.

Hallo Friends.

Due to other problems here (in real life) I missed this thread. Found it accidential this morning. :)

Just a short post, as I have to go to work next minutes.

I'm on a modular system, consisting of

• Master-Shield to set on a MEGA. It provides three channels of RS-485-Bus
  
• a common (Slave) Interface-Control-Board (ICB) which brakes out one (1) Arduino NANO - for use in most Panels
  
• some different specialized Slave-ICBs, which brake out one or more (ATM up to 4) NANOs (one of them is to connect a TFT for e.g. CDU)
  
• different Light-Boards (e.g. SAS, AAP)
  

I target on Pit-Builders, they don't can (or want) convert their flat into a workshop.

Everything is on a prototyping status. I think ATM, I can roll out a first batch this year.

The whole system (so is my intention) should be ready-to-use (do not confuse with RTF!) and bullet-proof. All boards provides Fail-Safe features, power supply and easy connecting. So any Pit-Builder can connect them (nearly) solderless.

For all those who interested and live too far away from Germany I'll commit all data to the community (as soon as I'm sure it works perfect).

@Gadroc: Thank you for your compilation of data.

Not sure if this is the right place to ask but it is breakout board related.

The Nano has pins 1-12, gnd and some other pins. Can you mix the connections to make more inputs i.e.

Pin 1 + gnd = Open cockpit

Pin 1 + Pin 2 + Gnd = close cockpit

Pin 1 + Pin 2 + pin 3 + Gnd = HUD day

And so on so one nano has about 77 combinations in dcs

Hey, Mr. Burns.

You are right. It's wrong here :)

But I'll answer anyway:

Based on what I understand your way (adding pins to get more outputs) will not work.

But you can use the original arduino keypad library.

I started to realize two MFDs with just one NANO. Also a CDU keypad is possible (not with the same NANO at same time).

As I remember right now, I contributed my (not finished yet) code-fragment already here: https://forums.eagle.ru/showpost.php?p=2916918&postcount=19

The code-example shows the way to build an 8x9-Matrix.

Don't forget to include Diodes into your Matrix's Layout (if you intend to press more than one button at same time).

If I find some time for that, I should post a tutorial somewhere here.... :book:

Meanwhile the manual of this library should help.

Otherwise: Thanks to DCS-BIOS we can connect an almost unfinite number of NANOs to DCS. So there are just a few special cases where a keypad makes sense.