The Project: To build a status reporter for a hottub located in the garden.
Background: I want to be able to monitor the status (water temperatur, pump running, water quality? etc) of a hottub from the house.

I'm using a DS1820 to record the water temperature and a PIC16F887 controller as the heart (I know its overkill but I have several to hand). This will collect the data (and other data as I get around to thinking about it) and send it via RS232 port and radio module to a receiver and display and possibly to a PC (or memory card) for logging for data analysis.

I want to be able to measure the current in the cable supplying the hottub so I can determine what it's doing. I don't want to break into the live cable (220V at a max of around 12A) so I'm looking at using a Hall Effect sensor. Does anybody know of a sensor I can use that I can just attach to the supply cable or will I have to use a torroid with the sensor mounted in a break in it and the supply cable running through it ? Ideally the output should be linear so I can determine what is switched on (idle, low speed pump, heater + low speed pump, high speed pump with no heater). I can calibrate the output in software, as long as it has differing outputs for the conditions mentioned.

In addition I'd like to use a logic level MOSFET to be able to disable the power to the hall effect sensor and DS1820. The MOSFET would be switched from the output from the PIC - the idea behind this being that the PIC will be in sleep mode and will wake itself every minute to take measurements and transmit them before going back to sleep. I'm doing this as I plan to make it battery powered with the batteries charged by a small solar panel (that will be a later question no doubt). Can anybody recommend a suitable MOSFET ? (supply voltage 5v and switch no more than around 100mA, probably a lot less).

Summary: I need a Hall Effect sensor to measure current at 220V and a logic level MOSFET to be able to control the power to the sensors.

(unless you have some better ideas?)

 

It sounds like a fun project.

If you want to get any accuract AC amps measurement I would google for "non contact AC current probe" or similar and look for a commercial clip on unit that normally connects to a multimeter.

 

...or will I have to use a torroid with the sensor mounted in a break in it and the supply cable running through it ?
(unless you have some better ideas?)

does this mean that you have a cable with 3 conductors inside, and by "a break in it" you are talking about hacking away the insulation and inserting a torroid? If so, what's wrong with that? I would do it.

If not, and you have 3 seperate conductors, why not use a torroid?

Google "current transformer"
they are not very expensive

would something like this help you? you could make a little rectifier circuit and voltage divider to dive you a 0 - X VDC output for a 0-X A input. You wouldn't have to sever your cable, http://www.google.com/products/cata...PAtgfohKz_DQ&ved=0CEAQ8gIwAQ&biw=1261&bih=819#

 

Inductive pickups don't require any insulation removal. The only requirement is that the pickup surround only one conductor, not both.

 

Inductive pickups don't require any insulation removal. The only requirement is that the pickup surround only one conductor, not both.

Right, but if both of your insulated conductors are encapsulated together inside an extruded rubber "insulation" then that will have to be removed to get at the single conductor. That what I was talking about, not exposing copper.

 

Right, but if both of your insulated conductors are encapsulated together inside an extruded rubber "insulation" then that will have to be removed to get at the single conductor. That what I was talking about, not exposing copper.

Yes, you are correct.