Clarification on Parts


 
D

Darren C.

TVWBB Pro
The parts list has listing for:
1 10k R-US_0204/7 R20 (use below)

Does that mean to use one of these?
4 10k 1% R-US_0204/7 R5, R16, R17, R18 Mouser DigiKey
 
Hmm. Well, I guess I'm still a little confused. I have a radio shack very near by, in fact I planned to go by there tomorrow anyway. So, I can grab the part. Looking at the parts list, I can't figure out the rest of the specs for it. Do you happen to have a part number or specs for it?

If you look at Bryan's photo, the probe resistors and the one for R20 all seem to have the same color code.
 
There are 5 x 10K resistsors in use

I used:

Mouser part #
660-MF1/4DC1002F
10K 1% 100PPM

Your digikey link would be a "like for like" replacement.
 
When it says "use below" I meant "use the part number below" so there should be 5 total, like there are in the mouser project. I didn't feel like finding a different 6 cent resistor part.

Pretty much any 10k resistor made in the last 30 years will be suitable for any of these parts.
 
I should have put more into that answer. :(

They are the same value, but not the same tolerance is needed for R20. R5, 16, 17 and 18 are all higher tolerance resistors - their true value is very close to 10K. R20 can be a lower tolerance resistor - a 5% or even 10% resistor would be fine. That's not to say that you can't use a high tolerance resistor for R20. R20 is just a pull-up resistor that holds the reset pin high until someone or something sends a ground to reset the system.

Why the higher tolerance? Well, those resistors are used as voltage dividers in the circuit, and having them very close in value to one another makes setting up the probes in software very easy. Otherwise you would have to measure each one manually and input the values. Using high tolerance resistors eliminates the need for this extra step.

And you can spend quite a bit of cash on high tolerance resistors.
digikey 9,999 - 10,001 for a 0.01% tolerance resistor, so a 1 ohm variance
digikey 9,990 - 10,010 for a 0.1% tolerance resistor, so a 10 ohm variance
digikey 9,900 - 10,100 for a 1% tolerance resistor, so a 100 ohm variance

So a 10% tolerance resistor could be off by 1000 ohms! :(

The takeaway - buy as sensitive resistors as you can afford for sensitive applications! Best bang for the buck occurs @ 0.1% for HM4 R5, 16, 17 and 18.

Besides, you don't want to waste a dollar on a $0.02 10K resistor.

Personally, I'm using these. http://www.digikey.com/product-detail/en/CMF5010K000BEEB/CMF10KQBCT-ND/2197140
 
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Matt is exactly right.

To reintroduce some confusion, R5, R16, R17, R18 are actually uniquely designed in that any tolerance resistor can be used. Their resistance can actually be measured in-circuit, which is something you can't normally do. So it doesn't really matter if they're 10,000.00 or 11,000, because you can just measure them once assembled (except for the thermistor) and enter the exact values into the webui for ultra-precise values.

I'll blow everyone's mind: The ATmega328P internally has a pullup resistor on the !RESET line so there's no need to put the R20 10k pullup on at all despite it showing up in every single ATmega/Arduino ever. I think the Arduino people added this at some juncture to get the USB reset to work more reliably in one case and now everyone just thinks they need it.
 
Thank you all for clarifying. I am no hardware guy, although I've been fascinated by hardware for as long as I can remember. So, this helps a lot. When I ordered, I just went through the list of parts and picked the supplier who had them in stock. I guess I overlooked this resistor while ordering and didn't notice until I began assembling.

Also, I want to thank everyone for creating and supporting this project. I can't imagine the hours you've put into developing, improving and supporting the project. I hope to get mine together this week.

Thank you guys so much for all you do.
 
Bryan,

I thought about doing this. I just want to verify the procedure.
1. Remove Power
2. Measure with Ohm Meter the resistor only while on PCB
3. Enter value in webui

Is that all? Or will I get a bad reading with it installed?

Nick

Bryan Mayland said:
Matt is exactly right.

To reintroduce some confusion, R5, R16, R17, R18 are actually uniquely designed in that any tolerance resistor can be used. Their resistance can actually be measured in-circuit, which is something you can't normally do. So it doesn't really matter if they're 10,000.00 or 11,000, because you can just measure them once assembled (except for the thermistor) and enter the exact values into the webui for ultra-precise values.

I'll blow everyone's mind: The ATmega328P internally has a pullup resistor on the !RESET line so there's no need to put the R20 10k pullup on at all despite it showing up in every single ATmega/Arduino ever. I think the Arduino people added this at some juncture to get the USB reset to work more reliably in one case and now everyone just thinks they need it.
Click to expand...
 
Nope, that's perfect. When no probe is plugged in to the channel you want to register, you can just use the ohm meter to directly measure the resistor while it is in place. The reason this works is one of the sides of the resistor is floating so it isn't "in circuit" it is just connected on one side and therefore you won't be reading the parallel impedance of the circuit but the actual resistor itself.
 
One more part question, my fan power phone jack was on back order and Radio Shack didn't have it. So,

1. can I proceed without it
2. can I rob the VGA out from my pi? I have to take it off anyway to fit my case. I applied a little heat to it and tugged on it. The solder didn't act like it wanted to melt too easily. So, I quit. I thought I better ask for advice first.

TIA,
Darren
 
I used the phono/rca jack from my rPi for my heatermeter. Works fine and lines up with the 3D printed case fine as well.

You'll want to use a solder sucker or solder removal braid to get the solder off the 3 pins.
 
Okay. Thanks. I tried the solder removal braid a little. The solder didn't seem to be melting right away. So I was afraid to leave the heat on it too long. I'll try it again.
 
Darren, cut about an inch of braid off. Take that and use the iron to hold it against the joint. The solder should come right out. Once the braid is saturated or the joint is clean then grab the braid with a pair of tweezers and pull the iron and braid away from the joint together.
 
Yeah the RCA part on the Pi is the exact same part as in the HeaterMeter parts list, just a different color. I have a difficult time getting them out too, but Matt's got the best solution I found too.
 
I desoldered my RCA. It was a pain. :(

Even once you get the solder out of the joint they will still have some solder in there. If you have a panavise handy that is the way to go. Put the Pi in the vise and while heating the pins slowly start to wiggle the connector out. I't'll be slow going, but eventually it'll pop free. A don't pull too hard.
 
I'll give it my best shot. I don't have a panavise. In fact, I'd never heard of them. But, looking on Google Images, it does look like it would be handy. I do have a pretty nice heavy duty vice attached to my work bench. I could use it to hold my pi while I'm trying to extract the RCA connection. I'll just have to be careful to not over tighten. If I'm not careful, I'll end up with Pi/2 or 2Pi, depending on how you want to look at it:).

I'm a little afraid that I may have tugged too hard on it already. We'll see. Once I get over that hurdle, I'm just about done getting the parts on. I've gotten the top side completed (other than the RCA). I was just about to start on the bottom side and thought I better slow down and deal with the RCA first.
 
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I don't guess my iron gets hot enough to melt the solder. I'm going to either have to cut the part off or get a hotter iron. Thanks for all of your help and suggestions.
 
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