DEF CON has a hardware hacking village where enthusiasts share their hardware and firmware and learn from each other.. We want a hardware hacking village for the P2, and it's right here in this thread. We're looking forward to seeing your neat designs and clever code!
Okay, I'll start. I do a lot of work with RS-485 and wanted an accessory board to do half-duplex RS-485. Here it is. I have boards on the way, so I should be able to build next week.
It looks like you are running separate rx and tx lines to the chip but 485 is half-duplex so I always have these joined, perhaps through a resistor if the chip is on 5V rails.
On the general subject of RS485, I've used many different 485 chips but the latest is the 65HVD1786 which not only is fault protected with 1/256 loading and 50mV hysteresis but handles +/-70V common mode which is important when it is operated as a pure 2-wire network without an "earth" which I have seen can create far more problems. Remember there's the common mode voltage and the fact that it senses the difference and also the inputs themselves form a resistive divider to its own ground anyway. No need for a ground or earth and if anyone disputes this I do the pencell battery signal source demonstration, flipping the polarity into the chip without a third wire. I decided I'd do a quick check to see if any other professional source backs this up and I was delighted to find sense prevails.
What I do have is a real solid earth separate from the common along and with the transzorbs etc.
Here's part of the RS485 I use.
edit: If you do an adapter board, you may as well implement dual channel RS485 since you can then also run full-duplex RS422.
It's a simple design for desktop experimenting. It works. In a production design and appropriate for the environment, I would add protection. That's not necessary here, nor is saving one pin at the expense of making code difficult for beginners to understand.
What's the part number of the SMT connectors on the P2 boards? I want to look at a datasheet. I'm actually interested in whether or not the footprint of the part includes the vias or if the vias are just added beneath the part. How would you stack these things? Do you just add a male-male pin header between the boards?
What's the part number of the SMT connectors on the P2 boards? I want to look at a datasheet. I'm actually interested in whether or not the footprint of the part includes the vias or if the vias are just added beneath the part. How would you stack these things? Do you just add a male-male pin header between the boards?
Okay, I'll bite... what do you do (or want to do) with RS-485? One of my next projects is a MODBUS (RTU) driver for the P2 so that it can be used in industrial apps. I did one for the P1 many years ago, but think I can be more elegant with what I now know.
I'm just feeding my curiosity. For example, your reference to MODBUS sent me on a feeding frenzy to virtual-serial-port.org. In my days at NASA I dealt with a lot of hardware that had RS-485 ports but never had a need or requirement to use them. We mostly used RS-232. Although my last project, the onboard ISS audio communication subsystem, had me working with a custom Harris TDMA protocol over a fiber-optic network. You seem to use a lot of hardware through RS-485. My guess was that it was either lighting controllers or audio equipment.
btw, I use RS485 a lot in datacomms especially for industrial and transport (airports, highways etc). Here is a video of using RS485 to connect to multiple Props and talking to each one individually or as a group by means of a virtual full-duplex console.
The modules were wired in close proximity but could be used over hundreds of meters.
Oh! To better answer your question, I'm working on a small P2-ES Eval board with the RV-3028-C7 RTC like the one on Peter's P2D2 board. I'll probably also add an extra I2C port with the 2 remaining pins. My plan is to provide a PC based interface application to the RTC and the extra I2C port similar to ELV USB-I2C dongle's GUI that Micro Crystal uses with their evaluation board.
btw, I use RS485 a lot in datacomms especially for industrial and transport (airports, highways etc). Here is a video of using RS485 to connect to multiple Props and talking to each one individually or as a group by means of a virtual full-duplex console.
The modules were wired in close proximity but could be used over hundreds of meters.
This is quite cool and you should add this to TAQOZ too.
After Jeff's and Michael's presentation yesterday, I'm thinking that I want to connect my WX DIP module to my Rev-B Eval board. This is my dirt-simple idea (based on some guidance from Michael). Once I've checked it, I'll order boards. If anyone else wants a kit, I could probably knock that together since I have to order parts, anyway.
Note:
-- This is for Rev B only
-- It won't work with the plastic enclosure
-- You have to sever a trace on the Eval PCB and add a 2-pin header
I based the design on Parallax's schematic for the SIP adapter for the Rev-C Eval. I'll wait a couple days, re-check, and then send the Gerbers to JLCPCB.
Looks good Jon. The WX module pinouts match 100%.
That will be handy to use with the older boards.
Edit: Ignore the removed comment (in case you got that sent by email already)... I checked the WiFi schematic- the DIP module DI & DO pins are directly buffered (in and out). No series mayhem! I think your design is good to go!
Does anyone have any experience with custom keypad assemblies? I'm building a replica of the keypad in the audio terminal units (ATU) onboard the International Space Station (ISS). They were custom built by Harris Corporation. I'm going to 3D print the panel and buttons and a build a PCB with the contacts but I need some guidance on the switches. Should I just tear about an old keyboard and savage the hardware or can someone recommend a source for keypad switches or techniques/methods/etc?
This is what the ISS ATU front panel looks like. It's about 0.568" longer than my Prusa I3 MK3S can print. I'll either have to shorten it a bit (which I don't like) or drive down the road and see if re:3d will print it for me on one of their Gigabots. Normally, I'd go to the Freeman Library and print it on their Gigabot, but, the PANDEMIC has shut off my access to their larger 3D printers and CNC machine for the duration. The reason I'm posting this in the Hardware Hack thread is because I want to see how much functionality I can get out of the P2. The plan is to have a working keypad, LCD, speaker and microphone. If I can get all that to work, I'll add the top PMIC/BPSMU connector. Hopefully, it will be an interesting educational prop.
ISS (International Space Station)
ATU (Audio Terminal Unit)
PMIC (Portable Microphone)
BPSMU (Battery Powered Speaker Microphone Unit) [salvaged from the Shuttle Program]
@CJMJ - you should really start a new thread as this one is really for "new ideas". But briefly if you don't use a custom membrane keypad, you could just mount tactile switches or even regular low-profile pushbuttons on a pcb and have the a plain stick-on polycarb membrane printed with holes in the metal front panel for the tops of the switches to just touch the membrane. I have switches that were designed for this purpose.
You can even print up a prototype membrane first using the heavy duty polyester laser label paper that is very durable and although not suitable for extended keypad use, would help you check the operation and artwork before committing and waiting for a more durable membrane.
Just start a new thread if you want to continue. You can leave a little message in the reply for the moderators to move this stuff to the new thread.
System
Posts: 45
Comments
Ken Gracey
Parallax Inc.
I use DipTrace.
On the general subject of RS485, I've used many different 485 chips but the latest is the 65HVD1786 which not only is fault protected with 1/256 loading and 50mV hysteresis but handles +/-70V common mode which is important when it is operated as a pure 2-wire network without an "earth" which I have seen can create far more problems. Remember there's the common mode voltage and the fact that it senses the difference and also the inputs themselves form a resistive divider to its own ground anyway. No need for a ground or earth and if anyone disputes this I do the pencell battery signal source demonstration, flipping the polarity into the chip without a third wire. I decided I'd do a quick check to see if any other professional source backs this up and I was delighted to find sense prevails.
What I do have is a real solid earth separate from the common along and with the transzorbs etc.
Here's part of the RS485 I use.
edit: If you do an adapter board, you may as well implement dual channel RS485 since you can then also run full-duplex RS422.
Harwin M20-7810645
-- https://www.digikey.com/products/en?keywords=952-3211-ND
I ordered standard 1.6mm thickness. Have been using JLCPCB recently; quality is good, price is low (even with stencil), and turn-around is fantastic.
I sometimes do board-to-board coms, but frequently am doing DMX output.
The modules were wired in close proximity but could be used over hundreds of meters.
This is quite cool and you should add this to TAQOZ too.
Mike
Note:
-- This is for Rev B only
-- It won't work with the plastic enclosure
-- You have to sever a trace on the Eval PCB and add a 2-pin header
I based the design on Parallax's schematic for the SIP adapter for the Rev-C Eval. I'll wait a couple days, re-check, and then send the Gerbers to JLCPCB.
That will be handy to use with the older boards.
Edit: Ignore the removed comment (in case you got that sent by email already)... I checked the WiFi schematic- the DIP module DI & DO pins are directly buffered (in and out). No series mayhem! I think your design is good to go!
ISS (International Space Station)
ATU (Audio Terminal Unit)
PMIC (Portable Microphone)
BPSMU (Battery Powered Speaker Microphone Unit) [salvaged from the Shuttle Program]
You can even print up a prototype membrane first using the heavy duty polyester laser label paper that is very durable and although not suitable for extended keypad use, would help you check the operation and artwork before committing and waiting for a more durable membrane.
Just start a new thread if you want to continue. You can leave a little message in the reply for the moderators to move this stuff to the new thread.
sure. create your thread and pm me the link.