Zero Crossing detection mehtods

[stempile]

This is a thread started to capture discussion around the subject of Zero Crossing and the methods used to detect it.

Zero Crossing is needed for the dimming controller design. Using a method to detect and feed this signal to a controller is important for all of the DIY dimming design. It will be a top discussed in detail with the Ren-C board.

ms

[P. Short]

I've updated the Renard Connection Instructions page in the wiki with information on this topic.

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Phil

[stempile]

The RenC Wiki

Option 1. ZC can be generated on the board, by connecting a 9VDC (unregulated or filtered) supply to Pins #7,8 or the RS IN/OUT RJ45 scokets.

Option 2. ZC can be generated on the board, by connecting a 9VDC (unregulated or filtered) supply to The "ZC In" pin (#3) of JP3.

Option 3. ZC can be connected directly to the board , by connecting a ZC Signal to the "ZC" pin (#2)of JP3.


In the wiki it mentioned DC supply to pull the ZC. Shouldn't it be AC? DC is constant with no zero crossing? If it is DC, then I am really confused and don't understand.

ms

[P. Short]

The wording there isn't the best. Perhaps it should say 'unregulated and unfiltered'. If you take an AC signal and run it through a full-wave bridge rectifier, the resulting signal half-sine wave is often called 'unregulated and unfiltered DC'.

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Phil

[stempile]

To Continue my education on the subject of unregulated and unfiltered DC I found this link:

http://www.zen22142.zen.co.uk/Design/dcpsu.htm

WikiPedia:
http://en.wikipedia.org/wiki/Rectifier

There are some pictures of different DC circuits that help bring home how this is working.

The section on full wave makes sense now. I was locked into a thought process that didn't make sense until seeing the pictures and description.

ms

[P. Short]

I've added a little bit more info on this topic on the wiki page.

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Phil

[bonuts]

Question about something from the WIKI regarding zero crossing options...

Method 1) Bring rectified ..... In this case you need to jumper U2-2 to U2-3

Method 2) Bring rectified ...... In this case you need to jumper U2-1 to U2-2

Looking at the REN64 BOM, I don't see a part that would allow you to use conventional jumpers (the little black or white plastic things you typically use on PCI modems, sounds cards, motherboards, etc). So is the idea to 'jumper' them with a piece of wire? If so, would it be possible to add a part to the BOM that would allow use of the little plastic jumpers? Thanks.

[P. Short]

I'll update the BOM later, but in the meantime I use something like mouser 571-41032390, and break off a 3-pin section to use for the 3-pin header. There are similar parts with less gold plating (or none at all), and in other lengths, on page 1190 of the mouser catalog 631 (Aug-Oct 2007).

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Phil

[MarkL]

If I had an external circuit which used a H11AA1 to generate my zero cross, does that chip have enough drive to send the ZC signal down a moderate (~50ft) length of cat5?

I'm thinking about how I want to hook up my Ren64 and Ren-C. I'm not using a Ren-T as it doesn't provide enough power (have a PC supply anyway). I'd like to use the H11AA1 to generate the ZC and send it down the cat5 to pin3 but I wasn't sure if it had the strength to handle that.

Thanks.
Mark

[P. Short]

If you want to generate a zero-crossing signal using H11AA1 and send it in through pin three of the RJ45, you need to find a source of +5V and send it to the collector of the H11AA1, and connect the emitter of the H11AA1 to pin 3 of the RJ45. The difficult is in providing the +5V (and associated ground) for this purpose.

I haven't tested in this configuration, so I don't really know how well it would work. I almost don't want to discuss this for fear of causing confusion.

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Phil

[Mrplow123]

If this is for a Ren64, and you are going to use a H11AA1. Why not just populate it on the Ren64 board in the provided spot, and not worry about sending it down a 50 foot cable? This is how I have both of my Ren64's setup and it works prefectly.

[MarkL]

I was just hoping to minimize wiring by getting everything into a single cat5. My controller will not be near the PC/power supply, so I was hoping to avoid having to send the AC to the controller as well.

[P. Short]

I would be just as worried (if not more so) about powering the Ren64 boards through 50 or 100 feet of Cat5 cable. If I remember right, the resistance of the 24Ga Cat5 wire is 25 to 30 Ohms per 1000 feet, which means that you would have about 2.5V drop in your 50 feet of cable if you are using one pair of wires (you have 50 feet of wire in the +5V, 50 feet in the ground for 100 total). Even if you double up the wires, you could still end up with a 1.2V drop (which is significant) assuming about 1A of current draw.

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Phil

[ErnieHorning]

I used the second method, as described in the Renard64 schematic, last year. You just supply half wave DC down the CAT5 and let the board detect zero crossing. You may have to add about a 100K resistor on the Vin line if your cable is more than about 30 feet. The capacitance of the cable tends to filter out the zero crossing point and you get erratic operation.

The advantage of doing it this way is that you keep the 120VAC inside the house and only send about 10 volt through the cable.

[MarkL]

I would be just as worried (if not more so) about powering the Ren64 boards through 50 or 100 feet of Cat5 cable. If I remember right, the resistance of the 24Ga Cat5 wire is 25 to 30 Ohms per 1000 feet, which means that you would have about 2.5V drop in your 50 feet of cable if you are using one pair of wires (you have 50 feet of wire in the +5V, 50 feet in the ground for 100 total). Even if you double up the wires, you could still end up with a 1.2V drop (which is significant) assuming about 1A of current draw.

That 25-30 ohms/1000ft is the number I'm familiar with too.

I definitely plan on doubling up the wires, and I'd hope that I don't draw anything close to 1A. (I'm not using PWM.) 50ft is probably longer than what it will turn out to be too.

If I use the 12vdc supply to power the board (like is done with the Ren16), I can tolerate some voltage drop anyway. The only issue there is whether that would be too much power dissipation in the regulator. Assuming 1V total drop between the cable and diode would put 6v across the regulator. If current draw is 200ma (again, not PWM) then that's 1.2W. I think the 7805 can handle that - definitely with a heatsink. (That's also if all channels are on full brightness for an extended period, which is unlikely for where I'm using this.)

[P. Short]

I think that you're OK if you are not using PWM. The current should be down around 100-150 mA. The voltage drop along the cable should be down around .25 V, so the drop across the regulator s/b around 7V. The power dissipation on the regulator should be under 1W, and you should be fine.

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Phil

[Mike78CobraII]

I'm a little confused on option 3. Does this mean that you would just supply power directly from a wall outlet?

[P. Short]

Where are you looking? There are a number of places that discuss different options or different methods, and I'm not sure which one you are looking at.

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Phil

[Mudsculpter]

I'm a little confused on option 3. Does this mean that you would just supply power directly from a wall outlet?

first,....Which board are you building?

[Mike78CobraII]

I am building the ren64 coop board, and trying to understand the zero crossing options in the the wiki.

[P. Short]

OK, I was a bit confused by the words "supply power directly". If you are referring to "alternative 3" in the BOM (bill of materials) on the renard64 page regarding the use of the H11AA1, the answer is yes. However, I do not recommend it, because I think there is too much risk involved in bringing 110 VAC onto the board (although people have done that).

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Phil

[Mike78CobraII]

That is what i thought. I feel comfortable with the high voltage going directly to the board as long as precautions are taken, such as using some sort of insulation to prevent it from being accidentally probed and of course unplugging it when being worked on or moving. Just use common sense. (Don't stick a fork in your toaster while it is plugged in.) And of course this would positively need a safe enclosure.

Thanks for the reply.

[jscheve]

Don't stick a fork in your toaster while it is plugged in.

Your not suppose to do that? How do you get the toast out then? :roll:

[Mike78CobraII]

Fill it with water the toast will float out.