ok, any suggestions (from the PIC-family
You need one with at least 3 x 16 bit counters
or timers that can act as counters.
Some further data: the main fuse is 40A, the group-fuses are 16A.
Let's say that I don't care what the meter-specs say (you're right, they're Chinese
), it's just one of the components in a system. 16A per group is max. The system needs to be able to read 16A of data coming from a group (although in our household, I really don't see any of the groups doing more than 12A at any given time. Our dryer is 2600W, so 12A at 220V and it is our winner so to say. Using 16A as max gives enough margin). Even if we run the microwave, washer, dishwasher at the same time while watching surround TV, we can't top 40A. (If we would, I don't want a logger - I would want an alarm
Off course, any one group could (theorethically)
use 16A. But please keep in mind that most households will probably be maxed out at 32A. And yes, it only has
to function here. If it serves anybody else - that's nice and I'm willing to share code and design.
Private residences in UK have the electricity supply fuse of 60A or 100A depending on age of installation.
So that's the design-criterium: per group 16A max, total system 40A max. Overall usage must be aimed at a regular (private) household (we truly -happily- don't use 40A normally).
Hmm many UK households have 32A ring mains for sockets.
I would like to get this thing going, so I would really be helped with some concrete design ideas. I'm not afraid of programming, not even assembler. However, the technical design needs to be simple, as I'm not an electronics engineer. Preferably I wouldn't need to get a printed PCB and just 'simple' components. And I'm not looking for stuff with a steep learning curve or pre-investments, because it will likely be a one-off. So there's the 'project-scope'.
Lets see you take 5V from Pi or other source (connect grounds of supplies if you use another one) to '+' pin 20 of each meter, take the pin 21's to a small board, which has a 1k resistor to ground on each separate signal, possibly add a buffer chip to protect the rest so it blows first.
Take the outputs of the buffer (or non grounded end of resistors) to counter clock inputs.
Excluding the counters the counters that could all go on a stripboard or breadboard easily. Very simple circuit.
Now let's say we would divide the 12 groups in blocks of three or four. Each to be serviced by their own 'capture-device' (no ARM - PDIP, it's a hobby-project). The readers need to be decoupled from the reading circuit (which is 12V).
The spec says you can use 5-27V DC why 12V and make life difficult? Just use a larger 5V PSU to power your extra board(s) and the Pi and keep things simple.
They say the SO output it is isolated, as it probably is a 30V FET or opto isolator transistro o/p
Opto-coupler? Which one? Circuit?
I would just put them through a buffer chip like 74*245 set for one direction.
The pulses need to be captured by the/a device. Again, 16A/group max, 3-4 groups per device. What device (no ARM), preferably PIC. Circuit?
I suggest you look on PIC site for suitable device with multiple counters, if you use a device with small number of counters, you comms handling and syncing with multiple devices will become arduous.
Integration of a RTC (which also needs to provide date/cal to Raspi) on the board, and communication between board and Raspi preferably needs to be isolated from the Raspi. (Ah yes, the Raspi is ARM too. I just like running Linux...
Components / circuits? I think these are basically the questions.
There are plenty of I2C RTC chips a battery, a diode a cap, a crystal can all be mounted on strip/bread board. The only possible place you need protection is the meter end, if all the grounds are tied together you dont need anymore.
I2C is not a necessity, could be SPI as well - which ever fits best. (Slight preference for I2C - but that is just because I already bought some components... ).
If you limit all components to be PIC and PDIP you have less components to look at. Lots of eval boards have connections on 0.1inch spacings so with components specced above
- larger psu
- strip/bread board
- 12 x 1k resistors
- couple of logic buffers
You have cheap parts to add to whatever micro and its 0.1inch spaced components. This is still hobbyist realm.
A board like I suggested could be added to that so about 50-60 pounds in total plus wires to cope with 6 channels inclduing development tools, and then see if you want to expand to 12 channels.
I think you will find restricting yourself to PIC and PDIP for everything will make it a hard task - time wise, board size and comms handling. I doubt anything less than PIC18 or PIC24 will have 3 or more timers that can act as counters, increasing cost of parts and board area (size of components), you may have to got dsPIC32. So far a quick search on microchip suggests that everything with 3 or more 16 bit counters is only available in TQFP surface mount. You will need to check a lot of datasheets as 16 bit counter is not a selection item as they assume timers are used for internal purposes or for driving outputs mainly.
Try this page as starting point http://www.microchip.com/maps/microcontroller.aspx
So to get your 12 counters will need multiple chips you probably want to synchronise on reading counters.
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading