BasicPI

These two diagrams show drafts of analogue data acquisition modules. The first is a 8 channel 24bit @30Ksps while 2nd is a 16 channel 12bit at 2,5Msps.

The ADS1256 is available for ca 5.- USD and provide 8 channels with 24 bit resolution at a sampling speed of ca 30ksps. This is very good for an ADC with this high resolution.

The faster ADC technique is achieved by using the ADC’s integrated in STM32 directly. These are 12 bits, but have a much higher sampling rate capability (2,4Msps).

I am not sure if I want to make both boards + I need to dig in a bit on analogue scaling & calibration options. I also need opto isolators that have limitations of their own. I also have the issue that the higher frequency of the 12 bit is of little usage + 12 bit resolution is a bit low for sufficient accuracy. Assuming I have space I could actually extend the 24 bit board with a few faster 12 bit channels as well.

One of the reasons I selected a PCM interface adding a digital sound connection was because it allows me to connect sound  to/from the MCU using I2S. As each GSM/GPRS Module also have both Ethernet & Wifi it is very easy to create a Mobile Home Phone Central with SIP Phones around the house. Using the fast backbone bus we can easily scale up to a quite large phone system. RS-X is a TDM protocol that is perfect for telecommunication, and bandwidth should in theory cover ca 60 voice channels on the backbone alone with 30-50ms algorithmic latency on the voice transport. Voice latency would actually be good because it is only static, algorithmic latency.

Keep in mind that this is 60 external lines only. Internal Ethernet/Wifi traffic will not be through the backbone. This design also have the advantage that we have an overkill in CPU power available in a truly distributed architecture.

This is a very interesting add-on capability to our Home Automation System.

Learning from my experience with a 168Mhz MCU interfering with a 180Mhz DC/DC I realize that I might need a similar option to separate the 4V PSU feeding the SIM808 on the module pictured above. In this case I would need a larger 2-3A coil related to 13 (4V PSU) above. This being a single side assembly I will add an optional connector for this on the back-side just in case.

Ethernet (W5500) already have a coil separating it’s 3.3V from the MCU.

 Raspberry PI Zero W also feed from the  same 5V – I need to add a coil option for this as well. What I will do is to add a connector that is shorted so that I can cut this and introduce an inductor if needed.

The last one is the 3.3V for the MCU itself. It feed from a 5V PSU that will feed several cards all running a 168Mhz MCU. I hope the linear regulator will do the filter job, but I will add an optional coil here as well – just in case.

I might also add some scope test-points + I will re-examin the SIM808 design – but after that I will order the PCB so I can start. I have to be realistic and expect that I will need 3-4 revisions before this module is working properly due to it’s complexity. I have evaluations boards we can connect to play with SIM808 SW – I actually need to get a new subscription with a few SIM card’s for testing.

This is a block diagram of the All-In-One Home Central. This is basically a merge between two PLC cards to create a smaller, mobile bread & butter node. I am not going to do anything on this yet – I simply want the MicroPLC modules up running first since this  is re-use of the same technology.

This also provide a full wireless RS-X switch as an alternative to the low cost wired one. The RPI module have sufficient juice for a secure wireless connection.

IoT is all about wireless connections these days. The main challenge is that providing sufficient security becomes a challenge becausse you need some computing power for secure encryptions – which easily drive cost and size. Myself I prefer to use secure wireless links to cover distances between buildings and floors, while I use more classic wired networks locally.

To enable this I need two new components to my Home Automation system:

This is a basic PLC module to provide 3 x External RS-X networks. I will create a all-in-one with these integrated later, but we can stick to the PLC backbone for now. Isolating everything will drive cost and size, but I want these 3 connections isolated because they will support long distance wiring exposing the entire system for lightning or pulses from other quipment. I will only get 3 networks on each card, but I can stack loads of cards if I need to.

 The second component is an Active RS-X Switch. This will bridge between an isolated network to a short distance non-isolated with 12V power added. With 4 connectors we can connect 4 devices or add passive switches to create entire sub-networks. We can also add another Active Switch by chaining these up to create larger networks.

The main advavtage is that we add power locally and don’t attempt to send DC power over any distance. Power is best transported as AC. We also create barriers where a lightning strike or other spikes will only have limited impact while we still can add low cost sensors in numbers. I created sensors and passive switch earlier that I will make upgrade revisions of.

I was finally able to test this on a pro lab with full 20A throughput. The small Fan started moving at ca 10A, but was still silent at 20A. We shorted and let the module take a bit of beating with no effect – it continued to behave. This turns out to be a very good programmable Lab PSU module. Well done.

A minor comment is that the module lack a calibration option. Both Voltage and Current are close, but we noticed a 0.3V difference to calibrated instruments. This could easily have been calibrated in software.

I had a few requests for these breakout boards earlier, so a few of them are on www.basicpi.com for sale at cost price. More of the boards will become available later – if you want to dive in early just watch out for proto-type offers or send me an email janvb@basicpi.org

I purchased this for < 12.- USD and tried it as a driver stage for DPS5020. It works fine. It is small and perfect for a 0-35V / 0-6A “bread & butter” lab PSU. The DPS5020 have a cut-off setting that I set to 6A. It cut’s the PSU if you by mistake allow more than 6A out to protect the driver stage. The driver is also short-cut protected.

• Driver PSU : 12.- USD
• DPS5005: 25.- USD
• Box : 17.- USD
• Mix: 10.- USD

That is 64.- USD for a single 0-35V / 0-5A and 101.- USD for a dual. And this Lab PSU will have far better spec than any of the “cheap” ones. Also keep in mind that DPS5005 is much smaller than DPS5020 as it hide the PSU inside the HMI unit.I notice that Input Voltage to DPS5020 variates with +/- 0.05 as I use the Driver at 5A. I will put a oscilloscope to see if I have ripple later.

I had to abort the test yesterday after ca 10 minutes because my load started to melt 🙂 – we have some awesome Lab PSU’s coming up. DPS5020 do have a small fan, but it has been silent so far.

Adjusting Voltage/Current on these modules are a joy- Just select V or A and turn the knob. Push the knob to change digit you adjust. With a MCU using ADC’s we have an accuracy on ca 0.02ich – which is pretty good compared to analogue PSU’s.

What we have not discussed so far is output filtering. With some of these giving 50V – 20A we will be giving 1KW out. That is 1KW that will spike back as 1000V with 1KW energy if we have coils/motors connected. We need to ensure that the PSU can protect both itself and the equipment we are testing.

The interface on the UART is Modbus RTU. I managed to translate the document from Chinese to English yesterday, so it is uploaded on the download page. Running the top-side app was straight forward on Windows 10. I had a bit of issues with antivirus installing it, so had to switch that off. The graphs are cool, but the window scale is a bit short and it only update once a second. Testing current under load was however a beauty. Using 36V in (3 x 12V/10) I had no problems with 10A out – or more correctly my load and test wires did get hot.

DPS5020 Protocol Specification 1.2 can be found on the download pages here.

Using UART/Modbus as interface it will be straight forward to create a custom HMI module to add buttons and display graphs on the box without a PC.

The diagram above show the minimum needed for any mains PSU. We need a On/Off switch and a fuse. This can be purchased as a single unit. The 2nd is the PSU itself that is available in numbers on the net in nice modules.

A 12V/10A module cost < 10.- USD and they can be connected to create more current or higher voltages. Using 5 modules you can create 60V/10A at a cost of < 50.- USD. Using multiple modules like this can save some cost, but it usually require more space. As illustrated in an earlier entry the Driver stage is actually more expensive than the DPS5020.

Please check the regulations of your country before connecting anything to the mains.