Easy way to trigger a picaxe from AC Signal?

[sodeaf]

Hey Guys.. I am working on a project with a 20x2.. I need to pull 2 VAC triggers from a machine. The AC voltage is 7.5 VAC.. and I need to convert this to logic input on Picaxe. Is there a simpler and easy way to do this other then using a $5 Opto-Isolator for each input?
I did some research and could not find an alternative.
I fairly new at this, and you guys are the experts.. So why not ask the best!



Thanks in advance....

Steve

 

[nick12ab]

Is one of the two AC rails connected to one of the DC rails that power the PICAXE? If not, then:

Or you can use a bridge rectifier:

 

[sodeaf]

Thanks for the input Nick..

I would say yes.. One of the AC lines is tied into the DC rail... The device I am working on has the following voltages coming from Power supply..
24 VAC
7.5 VAC
24 VDC
12 VDC
5 VDC

I am powering the Picaxe from the 5VDC.. As well the internal processor in the machine is using the 5VDC rail.. 12 and 24VDC are running motors. The Main board has multiple 40 pin ide style connections for all inputs and putouts. The signal I want to monitor is 7.5VDC from one of these harness's. Although I have found a spot to solder on the main board right before it connects to the triac that runs the AC light bulb and this is working for now. 5vdc high (On) low (off).. But I want to avoid all the extra work required to access this point on the board.. for I am looking to just tap into the easy accessible wire on coming form main board. I am looking at modding several of these devices.

Thanks

Steve

 

[nick12ab]

I would say yes.. One of the AC lines is tied into the DC rail...

Then use this modified version of the second circuit above.

The capacitor is optional, however if it is omitted then a quick read of the ADC pin might return a value that suggests that the ADC is off whereas a suitably small capacitor would allow reliable quick reads.