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Old 10th June 2010, 04:19 PM   #141
udailey is offline udailey  United States
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Reverse that.
Min setting = max attenuation = min Shunt LDR resistance = Max LED SHUNT current = max series LED resistance = min LED SERIES current
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Old 10th June 2010, 04:20 PM   #142
udailey is offline udailey  United States
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More current = more light = less resistance. Less resistance to ground = more signal goes to ground = less volume
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Old 10th June 2010, 04:30 PM   #143
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Quote:
Originally Posted by PJN View Post
Hi guys,

I

- I recieved 4 tiny little ceramic caps with my kits and I'm having trouble figuring out where two of them go. One came attached to a peice of cardboard and is labeled uc221, the other is loose with shorter legs and is labeled 100 on one side and K2J on the other.

- As added info could anyone tell me where the other two go, I installed them in C12 and C21, but would like to make sure before I'm done and fire them up.

PJN
I was in the same quandary and asked here. If I have it right, the first two numbers on the capacitor are its value and the 3rd number represents the number of zeros you'd add after the value. So, the 22 1 capacitor is 220 pico farads and belongs in the C12 position. the 10 0 labeled cap is 10 pico farads and belongs in C34. The one labeled 22 0 is a 22 pico farad cap and belongs in C10.

I am not sure, but I think I received only 3 of those tiny caps so you might have gotten an extra which is completely understandable when packaging up so many kits.

hth,

rick
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Old 10th June 2010, 06:23 PM   #144
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Quote:
Originally Posted by Lazarus500 View Post
...you might have gotten an extra which is completely understandable when packaging up so many kits.

hth,

rick
LOL

I got an extra 'dime' (10 cent american coin) in my shipment...
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Old 10th June 2010, 07:06 PM   #145
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Originally Posted by AndrewT View Post
it's easy to bridge connect the 4 resistors (2off 22k and 2off 47k) onto a plugboard.
apply 10 or even 60Vdc from top to bottom, i.e. to the junction of the two 22k and the junction of the two 47k.
Now measure the mVdc difference across the bridge, i.e. black probe to one 22k+47k junction and red probe to the other 22k+47k junction.

Now swap out one 22k for the spare 22k. is the mVdc difference bigger or smaller. Keep the swapped resistor in place and now put back the original 22k to replace the one 22k that was not originally swapped.
Is this the lowest or highest mVdc difference.

Now put in the two 22k that gave the lowest difference.
check the mVdc again.
Now swap the two 47k across with each other. Is the mVdc difference bigger? If yes return the 47k to where they were.

You now have the 22k:47k ratios at their closest match.
The pair of 22k&47k on one side of the bridge stay together.
The other pair of 22k&47k also stay together.

You can see how these pairs fit into the MyRef schematic. Both 22k & 47k have a common junction. It's those common junctions that must be maintained in the Howland current pump. Doing that gives the highest impedance available from that set of 5 resistors.
Thanks AndrewT for the wheatstone bridge tutorial. I, boneheadedly, mixed my resistors together not realizing the matched pair were separate. I used my super cheapo multimeter to measure and was able to ID the matched pairs in 2 of my 4 kits. The other 2 kits weren't so clear with my meter. I used the bridge to check out and optimize the unknown kits and then went back to the 2 kits I was confident in and checked them. Although I am sure they were well within tolerance, I was able to further optimize R5/R6 and R8/9 with the bridge. I simply taped the resistors to the benchtop and using alligator leads and a 12vdc supply (everyone has one of those in their garage, right?) to mix and match until I had the best combos. It took very little time and should maximize performance. Highly recommended.

thanks,

rick
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Old 10th June 2010, 11:37 PM   #146
AndrewT is offline AndrewT  Scotland
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I am glad my description was buildable and operable.
I'm not quick at drawing up sketches and schematics, so I tend to describe and sometimes it comes out garbled.
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Old 11th June 2010, 01:02 AM   #147
sabre66 is offline sabre66  Canada
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Originally Posted by udailey View Post
Every LM318 I ordered was a Nat Semi. I had to order from no less than 4 different sources to get them all for some reason. Anyway, all Nat Semi. My LM318 look like your LEFT IC with only an etching in the surface and no silkscreen on the top like your RIGHT IC.
So from what you have said we can probably rule out a dead LM318 but we can rule IN that the proper LM318 will do the trick. I honestly wonder if the silkscreened one is a real Nat Semi chip. I know I sent it to you but obviously I am not in the fake IC business and obviously you have two supposedly Nat Semi ICs of which only one works.
Your other 5 that DONT work: Where did you get them from and do they look like the silkscreened one?
From what I remember from the previous buy and from earlier posts in the original thread a lot of people have had clicking trouble. I wonder if your home voltage is lower than normal and if for some reason its fine for the one IC and right there on the line of fine/not fine for the other ICs.
Troy I think you have helped a few people with this. Wasnt there a resistor that folks lowered the value of when they had the clicking trouble?
The sink is just way to small and the sinks on your Caddocks are going to let your Caddocks fry. This is basically a non starter. If you leave in those heatsinks they will fry if they have not already. Both the LM3886 and the Caddock but the Caddock first.
I also wonder where is the 470k resistor near the opamp on the left side. Maybe you mounted it below.
All 5 lm318 look like the silk screened one. I'll get different sinks on to those caddocks right away, and I'm building a heat spreader as we speak for the 3886's.

Thanks
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Old 11th June 2010, 03:40 PM   #148
PJN is offline PJN  United States
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Thanks Rick, for the explaination of the esoteric world of cap labeling, very helpful.

PJN
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Old 11th June 2010, 05:17 PM   #149
AndrewT is offline AndrewT  Scotland
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I checked all my inventory.
Uriah, not a single error. Brilliant!!

I pulled out the 3off 47k and the 3off 22k
The 2000 count DMM set to 200.0k could not tell the odd one apart. the LSB was flickering and could not reliably resolve which was different
Series coupled the three 47k and applied 590mV across the string.
Measured the voltage drop across each 47k, 196.2, 196.2, 197.0
Pretty obvious which is the unmatched of the three. and also why the 2000count DMM could not tell them apart. Only 0.4% spread between all three.
set the 197 apart to become R20.
strung the three 22k together and measured the voltage drop across each.
188.0, 187.7, 187.6. Again the 188 was set apart to become R43.

Now set up the 4 resistors in bridge formation.
Applied 12V across top to bottom. VdiffA across the middles ~1.0mV.
Increased the supply voltage to 63V and VdiffB=8.5mV
Swapped the two 47k. Vdiff=1.0 and slowly stabilised to VdiffC=1.6mV The heating effect of 115mW dissipated between all 4 resistors was having an effect.
Now added a 1r0 between the two top resistors.
Clipped +63 to one side of 1r0, short wait till stabilised VdiffD= -2.3mV.
Shorted out the 1r0 and VdiffE=-1.6mV
Moved the +63 to to the other side of 1r0. VdiffF =-0.9mV.
Shorted out 1r0, VdiffG=-1.6mV

The shorted 1r0 in the last two arrangements (VdiffC=VdiffE=VdiffG) confirms that the VdiffC=1.6mV
VdiffF=-0.9mV is the minimum Vdiff. This is the best ratio match for the 22k&44k for the bridge.
Now as a final check I add a second 1r0 parallel to the first to insert the 0r5 that our modified Howland CCS uses. With 0r5 shorted out Vdiff~-0.6mV and with 0r5 in circuit, Vdiff=-0.9mV Notice I am starting to get some variation in results as we close in on precise Wheatsone Bridge balance.

I can see from these last two results that adding 0r5 changes Vdiff by 0.3mV whereas changing by 1r0 made a Vdiff change of 0.7mV This confirms our readings are about right.

If I wanted Vdiff=0.0mV with 0r5 in circuit, I would need to add ~1r5 to the other side of the bridge in series with the other 22k.
Well, let's test it.
I now have a bridge with one side consisting of 0r5 + 22k + 47k.
The other side consists of 1r5 + 22k + 47k.
Vdiff=+0.1mV. The correction resistor of 1r5 changed the Vdiff from -0.6mV to +0.1mVI short out 1r5 and the Vdiff returns to -0.6mV
I have added a slightly too large correcting resistor.

No worries. Here's why.
As supplied by Uriah, his matched resistors gave a worst case Vdiff=8.5mV and a best case Vdiff=1.6mV simply by swapping around the components as supplied.
Then when 0r5 is added (to mimic the effect of the Caddock 0r5 in MyRefC) we find the better side to add it to. We reduce the Vdiff to ~1mV.
We find a correcting resistor of 1r5 to be too big.
That 1r5 is only 0.007% of the 22k. I will leave Uriah's supplied resistors as he sent them.
Trying for better than 0.007% is a waste of my time and yours, particularly since no one came back to answer my two questions.

But one final comment. Vdiff best = 0.6mV and Vdiff worst 8.5mV. That is worth the few minutes it will take to find the right way to combine them.

Where do we fit them?
Take the side of the bridge with 0r5+22k+47k
These resistors become R3, R8, R9
The other side of the bridge uses up the two remaining positions of R5 & R6.
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Last edited by AndrewT; 11th June 2010 at 05:27 PM.
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Old 11th June 2010, 06:36 PM   #150
udailey is offline udailey  United States
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Andrew
Awesome post! Thanks for the education!
Uriah
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