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[shobley]

I have one of the newer AM486 appliance modules using a surface mounted 14-pin SONIX microcontroller and the MCR 100-B SCR to switch the relay.

I thought I had it sussed-out last night as the control pin on the uController was plainly connected to the SCR via a couple of caps and resistors. (Pin 4 IIRC).

I hooked up my multi-meter, but could not see a change in pin state when the relay switched, so I assumed that it must be a pulse (too fast for my meter) that was causing the switch. A quick check on the Vss/Vdd pins showed that the uController was running at 4.1v - safe enough for my USB scope - so I hooked it up, switched on, and managed to fry the protection diodes inside the scope  and create a wonderful buzzing sound into the bargain.

My beloved MCC 1208FS DAQ now bricked after 5 years of faultless service.

I suspect that I'd shorted something out while moving the disassembled module to my bench.

Anyway - I am looking to modify the relay switching function of the module to work with an Arduino. I want to use the device to switch a toaster oven on and off under external control - effectively bypassing the X10 side of things completely.

Does anyone know how the switching function works?
Is it a pulse, or something else?

And how dangerous are the levels inside these things?

Thanks,
Steve

[Brian H]

I did a partial schematic of the new model, when doing the momentary dry contact output mod.

4.1 Volts is about right for the supply. Mine was 4.2 volts. There seems to be a low voltage Zener clamping it.

The SCR is fired by a single pulse on the gate and the cathode of the SCR is on common. The anode connects to the coil of the ratchet relay. With the other side going to the neutral side of the AC input. There is a TNR 07D221K suppressor across the coil.

The coil is about 56 Ohms so it is a brief but strong current surge. As the 56 Ohm coil is basically across the line for 1/2 cycle.

If the am I on off sensor circuit does not see the output state change it may fire two more times in an attempt to switch the ratchet mechanism.

OK now for the warning. Like many X10 modules they are power line derived supplies and have 120 volts AC floating on many signal and DC lines.
In this modules case. The COMMON of the board is connected directly to the 120 volt AC power line input. The the negative terminal of the 100uf/10V power supply cap is the AC Power Line Input.     

Good chance your USB scope got a 120 volt hit back to ground or neutral through the common of the PC Board.

[Brian H]

You maybe able to come up with an optocoupler or something. That would allow you to externally pulse the SCR and not have 120 volts AC floating around the external trigger connections.

[shobley]

Dang, that's one scary board...

Thanks for clearing that up - I was lucky not to take out my computer as well.

So you think that if I were to hook up an optocoupler running between the Vss/Vdd of the chip and then use an external line to pulse the (0-4.1v?) this would be enough to trip the relay?

Is it just pulse-on, pulse-off?

I'll have to post some photographs tonight of the connection points - just to get a second opinion before I do anything...

[Brian H]

The switch is a alternating type.
One pulse should change it from On to Off or Off to On.
If it is On it will ratchet Off. If it is Off it ratchets On.

Since the microcontroller doesn't want to pulse the coil if the switch is On and it receives an X10 On. It has a sensing circuit connected to the outlet and doesn't pulse the coil if the switch is already in the state the command was for.
It also has to trigger the SCR when the Line is in the negative part of the AC cycle or it may not conduct.

The optocoupler would have to pulse the trigger on the SCR and it would then toggle the switch on or off through the coil.

The older appliance modules had a jumper you could cut and add a local trigger switch. I don't think the new ones have that option.

[shobley]

(Again) Dang, that's a complex bit of kit. I might just go looking for a relay I can mod instead.

I have some old appliance modules kicking around somewhere - I might open one of those up and see if it's any different.
Failing that (and if I can find it), I have a serial computer interface too - I know people have hooked these up to Arduinos.

Steve

[Brian H]

It will be quite obvious if you have the older one.
Through hole dip style controller and completely different layout. Along with power supply. Though still a hot chassis.