# 12DC Sockets

Discussion in 'Automotive Electronics' started by Muttley600, Jan 16, 2012.

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2. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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RMS, TRMS I have to say something.
RMS means Root Mean Square and there is a Calculus formula for it. T means True

If we had a 12 V DC signal and a 12 V RMS signal they would obey ohms law for heating a resistor and they would be equivelent voltages for heating a resistor.

Thus a Thermal based detector is best. Will they put one in a handheld DVM? Nope, too expensive. In any event a TRMS detector has a frequency response associated with it and it may have options like AC and AC+DC which complicates the whole mess. There are some non-thermal ways of doing true RMS with limitations.

The average Joe is only concerned about measuring sine waves, so the multimeter uses a precision recifier and a capacitor to average. It multiples that number by a Fudge Factor which becomes the RMS value of a sine wave.

Joe Industrial electrician needs a TRMS meter to deal with SCR power controls.

Joe Analog Engineer needs one or at least a good AC meter to deal with audio which has a fairly good frequency response.

Joe RF Engineer might need TRMS out to 10 MHz or more, hence he needs different tools. In fact, I have a TV antenna/Cable signal level meter that does just that. It has the ability to tune and measure digital and analog voltages.

3. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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In Mutt09 push GND to see where the GND reference is then it might make some sense.

A simple stack of two sources might be better for a first cut. A sine wave source in series with a DC power source.

With AC there are so many ways to describe a sine wave such as; zero to +peak, zero to -peak, DC offset, peak to peak, RMS; frequency

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5. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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db's or decibels is an entire topic all to itself. The concept is used in the Richter scale for measuring earthquakes and it can be used with power or voltage, It needs a reference. When designing amplifiers, it allows the gain to expressed in db. Each stage adds rather than multiples. I can't imagine the mess when trying to find the loss of a CATV/MATV distribution system without db. A tap has a loss. Cable has a frequency dependent loss per foot, taps have a loss, splitters have a loss, connections have a loss etc. Yuk!

6. ### Muttley600New Member

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7. ### Muttley600New Member

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doh, I've done it again, kept refreshing last page & you'd moved on......I thought you'd stopped talking to me

8. ### Muttley600New Member

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????? Am I being thick

ok, found it on scope but I was expecting multimeter to read it?

We might as well keep going with this sim, I've got to understand it sooner or later

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9. ### Muttley600New Member

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ok, we'll leave that for now then

Think I've caught up again

10. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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Looks like someone is making a couple of bucks wouldn't you say? https://shop.allion.com/Product_List.asp?iGroupNum=4

Look at the USB voltage/current test adapter.

Which is effectively what I'm proposing is needed. I just went a bit further and provided current signal conditioning.
Graham can build one and we can all participate in the total cost? I would not mind such a device at all. A PC board with V/I test points and signal conditioning.

A 5V wall wart would provide the power for the signal conditioning. No needs for the shunts shown in the pictures. Two small test points on D+ and D- too so you can find the resistor values in the special cables and maybe a header, so that they could be inserted?

11. ### 4pyrosWell-Known MemberMost Helpful Member

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12. ### Muttley600New Member

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\$130 bargain.lol

Cant we just get a digital readout if it's only off two wires or is that just work for the sake of it when multimeter could read two metal sockets onto them, in fact you could just leave breadboard pins through box & read all four

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13. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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That isn't three resistors: It's a shunt or a thingy wher you can connect a meter.

Graham: In post 560 and with the ground reference, you can see clerly that the DC value is 1 Volt. The Average value of a sine wave is zero, so your measuring from the zero point (GND) to the center of the sine wave in DC mode.

Use the cursors to determine the peak to peek value of the AC waveform and we can try to make some sense of the AC value. If the meters are not TRMS it ends up as nonsense.

Two sources in series would make it easier.

14. ### cowboybobWell-Known MemberMost Helpful Member

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Been off-line for a bit. WEB acess went kaput.

Anyway, here's where I left:

Let's try this. And it's generally an AC signal on (or with) a DC bias.

Let's say your 6' tall. There's a 6' door in front of you that is also 6' tall. Except that the bottom of the door is 3' off the ground (Gnd).

You walk towards it but cannot get in because you're lower half is 3' below the bottom on the door. Your upper portion could get in, but your lower portion would be blocked and left behind.

Now let's say we can apply a gravitational bias that elevates you 3' above the ground (Gnd).

Now as you walk forward ALL of you can pass through the door just fine.

The same thing happens in a circuit. A signal (sine wave, for instance) might not ALL get through a circuit (an amplifier, for example) because a portion of that signal "swings" below ground (Gnd, or zero potential). By elevating the entire signal (biasing it) with a DC potential great enough to get ALL PORTIONS of the signal above ground (Gnd) allows all of the signal to get through and be amplified.

And, of course, there are other uses for biasing, but for starters, this is one use.

Make sense?? (Did to me when I wrote a few hours ago. Still sorta does...)

KISS: Yeah, they're pretty proud of their stuff...

Give me a little bit to catch up.

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15. ### Muttley600New Member

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Anyways, why isn't my virtual meter picking up 333.3mVDC?

Made perfect sense CBB, so that explains bias

Nice to see your still around 4pyros

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16. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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The problem is your measuring low currents at low voltages. Most DVM's unless they are of the feedback type have a significant resistance. Your 200 mA scale might drop 0.2 volts or it could drop more. Depends on the meter. The idea with the hall effect sensor is that the resistance will be low.

We have to measure 0.1, 0.5 and 1 Amp at 5V without dropping too much voltage. I think with your suggested parts which can plug into a 0.1" spacing breadboard, you can use a simple SMT breadboard for the allegro device. Then you just need a power socket. These should be available from sparkfun.com. Your multimeter can also be used for other things too.

17. ### cowboybobWell-Known MemberMost Helpful Member

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Graham:

Construct this circuit (AC and DC sources in series).

View attachment 61188

The numbers you get will make more sense.

Don't forget that R1 and R2 represent a voltage divider: Both the ACV and DCV signals will be exactly HALF of what the two power sources are putting out.

Alternate between AC and DC "Coupling" and observe the action of the AC signal. (Make the "trigger" "Source" VF1)

(Hat off to KISS for suggestion)

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18. ### Muttley600New Member

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Back on computer, just had tea, so the 1v is the lift to center of wave off gnd & the 333.3mVDC is the distance between bottom of wave & gnd, I'll get it slowly

no, that's just me, you'll get used to me I missed the word link out, the first link you put up didn't work

are you saying the meter will affect the reading but this hall thing, how does that work then?
how would we be reading it, I need to go read datasheet don't I

This is meter I have

So far I've only used before starting to learn, Amps/volts/continuity, then since being on here I have now used Ω as well

Can you narrow that down for me, theres loads

I wasn't looking to make it on breadboard unless we are doing that for testing it to start with, that was the only thing I could find

It would be good to make one in box

what did you think to my £2 batt usb charger?

Last edited: Feb 16, 2012
19. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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Copy and paste this link http://search.l-com.com/search/keywords-usb--page-6--sort_by_field-Price_Low_to_High--x-0--y-0

for a list of USB stuff

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20. ### Muttley600New Member

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Will have a go tomorrow as it's nearly time to walk bobby, off work again next week so what I don't get this week I can spend more time on next week
I'll start, I've got 10 mins left

& so far I have resisted asking how you can have a battery & another source inline because I'm expecting you to tell me that it is possible even though my logical brain is screaming at me

21. ### KeepItSimpleStupidWell-Known MemberMost Helpful Member

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Electro-Tech is mucking up links. It's a new think. It's coping them to it's own space, but sometimes it doesn't work.

If ET mucks things up use these tags around the links: [plain]link[/plain]