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Old 27th February 2012, 04:48 AM   #481
_Wim_ is offline _Wim_  Belgium
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Also ensure your "measurement" card is not used as the "default" sound card for Windows. Otherwise every now and then windows interferes messing up your measurement...
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Old 24th March 2012, 06:24 PM   #482
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I just ordered the board from Pete. Looking forward to using it for my testing.

I do have some doubts as to the MDMV0000 part. It is expensive, very expensive!

Isn't there any way to replace it with another part? It just seems to be a simple voltmeter 5v powered. I have several (a dozen or so) assorted voltmeter panels which would serve the purpose of displaying voltage. If a 200mV display is required, I can either find one (should have one) or source it for less. Connections can be made with leads.

If a 200mV with 0.2% accuracy, 5v module is required then there are plenty of chinese backlit displays of similar size for as little as 6 euros shipped.

Last edited by Alexontherocks; 24th March 2012 at 06:27 PM.
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Old 24th March 2012, 06:43 PM   #483
AndrewL is offline AndrewL  United Kingdom
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You don't need the meter if you have decent external meter, its very convenient, however. And, if you just want FFT's which are relative measurements then you can miss off the meter, the true RMS chip and the logic gates altogether, that will make it must cheaper to build.

I also seem to recall the free shipping break points and the needs for two orders, one from Digikey and one from Mouser, means two lots of shipping costs, this make the meter less expensive in reality than it really is.

The meter is a true RMS at all frequencies so you need to source one that's similar, a lot of cost effective DVM are only true RMS at 50Hz.

Andrew

Last edited by AndrewL; 24th March 2012 at 06:49 PM.
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Old 24th March 2012, 06:49 PM   #484
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the meter is expensive per se. I think the price is 60+ euros. For a Voltmeter that is expensive.

I thought the AD536 IC did the true rms work and simply sends a voltage signal to the panel meter for basic display purposes. The module itself by red lion does not seem to feature any true rms circuitry, but I may be wrong.
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Old 24th March 2012, 06:58 PM   #485
AndrewL is offline AndrewL  United Kingdom
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Yes the LCD is just that a display, I edited my posting after you posted, you could remove various bits if you don't want the meter; apologies if it wasn't clear.

But as I said I don't regret buying mine and I did contemplate not adding it. Also, you'll find that once you hook it up to a sound card that the various input and outputs values you need to drive the box to full scale mean you end up tweaking the sound card volumes lower than you expect, it only needs 500mV for full scale; having the meter gives you a point of reference otherwise its hard to know when your driving the ATEST box to clipping.

Also to get the noise floor down on mine I ended up shielding in the box, you need to blank the hole off in some way, I suspect.

Andrew

Last edited by AndrewL; 24th March 2012 at 07:04 PM.
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Old 24th March 2012, 07:10 PM   #486
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Thanks for the reply. I now have confirmation that the display is just a display. If it is for reference during tweaking then I can find the least expensive compatible solution.

I hope no other component is that expensive or that hard to find.

Maybe an updated BOM could be useful for the forum if things have changed since the birth of the interface.
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Old 24th March 2012, 07:18 PM   #487
AndrewL is offline AndrewL  United Kingdom
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What I would do in your case if add a couple of 4mm banana plug sockets to the front panel and then plug in a DVM there so you can see what you are feeding into the system when you are setting things up.

The rest of the stuff is pretty standard I think we figured out some of the op amps could be upgraded but you'll be Ok with the ones Pete spec'd. I did have trouble finding the coupling caps but I wanted more uF to get the roll off out down lower.

Andrew
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Old 24th March 2012, 07:24 PM   #488
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Great! I'll just add IC sockets to allow for upgrades in the future.

The plug are actually a great idea, better yet those spring loaded connectors (as seen on amplifier backpanels). I like the idea of a standalone RMS meter so I may just complete the design and provide space for a battery pack and a switch.
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Old 24th March 2012, 07:25 PM   #489
AndrewL is offline AndrewL  United Kingdom
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If you look further back a bit you'll find I posted a summary of all of the tweaks, least I think I did, if you can't find it I'll repost.

Andrew
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Old 25th March 2012, 08:59 AM   #490
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Default different Voltmeter

Hey there, i used a different Voltmeter in my build, the EA-VK 1000 from a german distributor.
Its 26, works well but needs a few changes to the ciruit. (i didnt use U2, R1,R3,R8,R10 and i connected the SW4A directly to the voltmeter, wiring it with short leads from the vm to the board since the connector doesnt fit)

EA VK1000 - 3-stelliges Mini-DVM bei reichelt elektronik

this might be another option for you,
cheers
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