IO Expansion Card

Question

I use a Raspberry PI for my home automation. Security, Heating, Cooling and Irrigation.

I use a mix-and-match of IO cards and relays. Wiring is a mess.

I looked for an compact IO card to do all I needed and could not find it, so I designed my own. I am thinking of trying to sell it.

The card is a stackable HAT, it passes through 23 GPIO's from Raspberry and it adds another 18 of it's own.

Twelve of the 18 GPIO's can be configured as 12 bit ADC's. It also has eight on board relays, eight optically isolated inputs and one DAC output.

Timers lurch in the dark, can be programmed if needed. STM processor on board with PWM and lots of other I/O resources.

Q1. What are the restrictions of using the Raspberry logo on HAT cards?

Q2. Anybody thinks this card is a good idea, or it's just in my head?

Robert Peter Oakes · Answer

I would be sure to add a disclaimer regarding Mains operation then to cover your ^&%(%. and activly discourage people from using it directly with mains. (Provide an alternate option for that as a simple external MAINS relay in a box or something. I personally use SONOFF Relay WIFI units, there based on ESP8266 chips, are really cheap and have CE certificate. for many models. Thould would easily cover the "Mains side of things and easily to integrate with the PI using MQTT or other methods.

Workshopshed · Answer

To call something a "Hat" it needs to meet the Hat Spec. This includes an EEProm and device tree so that it can self configure. See https://www.raspberrypi.org/blog/introducing-raspberry-pi-hats/ for more details.

Robert Peter Oakes · Answer

What are the specifications for the inputs and outputs, the Relays themselves are probably rated for mains but a HAT should NEVER be for so many reasons.

You did not specify what the analogue IO is ranged at. Can you provide more details ?

mbeffa · Answer

Sorry to call it a HAT. I will check the specs. The device can self-configure. The on-board processor can emulate an I2C memory and respond accordingly.

mbeffa · Answer

The opto-isolated inputs use standard Toshiba TLP293TLP293 optocouplers

The on-board processor is from ST Micro, STM8L151 - GPIO pins are connected directly to the expansion connector.

If the price is right (under $40), why NEVER have so many features? Use only what you need.

The relays and relay connectors are rated 10A/250V.

There are 12 ADCs, 12 bit and up to 1Msps each.

Due to connector limitation, the 12 ADC's are part of the 18 GPIO's - mix and match as you wish.

All I/O's are memory mapped through the I2C interface. The card looks like an I2C EEPROM.

I did not mention that there is also a DAC output, up to 7 timers, PWM and other stuff that we do not plan to support, at least in the first phase.

Robert Peter Oakes · Answer

thanks for the fast response and good information.

My Only remaining query is with the relays

Are you claiming and stating that the board supports 10A at 250V or simply that the relays are rated at that.

Many of us TMs on the E14 community have had to step in with advice and more when it comes to designs of boards claiming to support Mains and High current, specifically mains voltages.

Due to the nature of how a HAT connects to the PI and also the type of people that would be targeted for a HAT, we always advise, sometimes quite strongly that the approved volts be no more than about 30 or 40 volts. basically put, to have mains on a HAT is downright dangerous and a disaster waiting to happen. and there are so many better ways to control mains devices from any microcontroller.

mcb1 and I have advised on many projects here on the E1 community when it comes to this kind of safety issue.

If your not telling people you support Mains on the board, then great but then I would suggest a warning o folks not to do it, simply because the relay says it can (A common mistake many consumers make)

mbeffa · Answer

I am claiming the relays and the connectors to get to them are rated 10A/250V.

(Songle relays used by all relay boards)

.

I am using the relays to control sprinklers and heating/cooling of the house. All run at 24V.

I would not run 250V or 10A into the board, but if someone wishes to do it, the relays claim to take it.

Such a small board should not be used to drive industrial control equipment requiring many amps.

The main application should be home automation, all 24V systems.

The board will come with a browser interface for all I/O's, running on Raspberry's web server.

mcb1 · Answer

I would not run 250V or 10A into the board, but if someone wishes to do it, the relays claim to take it.

The issue is not the relay but the pcb layout and sizing.

A properly designed board for 230v will have cuts to reduce tracking across the board surface.

The connectors, pads and track widths will be suitable sized to cope with 10A current, regardless of the voltage.

mark

Workshopshed · Answer

A separate box with IEC sockets and plug would be a good approach.

Robert Peter Oakes · Answer

Yes for sure, but I would also have a relay in that box with the IEC socket. the local one on the hat can drive it safely with low voltage.

mbeffa · Answer

High voltage specs on the board have been reduced to 24V and 4A.

Another card is in the works with true 250V/10A capabilities and industrial specs (4-20mA and 0-10V in and out)

Previous card is now available at sequentmicrosystems.com