CategoryVisual Diagram Included

µC Prototype JFET Vpp/Idss Tester — scalable to 20-50+ at a time Phase 2: The 12 Little JFETs That Could and my First Etched PCB

I’ve been experimenting with making PCBs. I’ve always wanted to, but it’s something that I’ve never actually had the chance to do. I went through many a lot of iterations trying to get the toner transfer method to work.

In retrospect my big mistake was grabbing Kodak’s Ultra High Quality inkjet glossy photo paper. Photo paper can work well, but not this 10.7mm thick stuff with a plastic back. I didn’t actually have an iron, so I tried everything I could think of and only wound up going from almost no toner transfer to getting around 80% of the toner transferred with lots of broken traces. I started with a ‘hobby iron,’ which didn’t have enough contact area or enough heat. I was going to use a hobby heat gun, but I couldn’t locate it. I went through probably around 20 sheets of the stuff. I tried heating the paper from the back lightly with a propane torch, which actually gave me some results but only near the center. I heated the copper layer with the torch first, and actually destroyed a couple boards that way by applying too much heat from the torch. I did wind up getting vastly improved transfer this way as I rolled a piece of ~1.5″ aluminum pipe over it and VERY gently heated the paper with a torch.. but I was still left with an unusable amount of transfer.

So I was going to buy baking sheets today (aka cooking parchment, apparently) as I read that had excellent qualities for laserjet toner transfer. But before I ran to Walmart I was in Walgreens which is much closer to me. I picked up their glossy ink jet photo paper thinking I couldn’t do much worse than what I had already done. I learned that there were many thicknesses of glossy photo paper (The More You Know..) and this material actually had a paper back so it should fall apart in water and require less work for removal. I bought a cheap $18 iron while I was there. I’m not sure if it was the iron or the paper (but I’m betting it was mostly the paper with the iron not exactly hurting matters) but I got usable transfer on my first try. There was one little area where a large power trace was broken. I had the foresight in Walgreens to pick up fine-tipped Sharpies, so I scribbled in the broken trace and dumped the board in some Ferric Chloride.

<img class="wp-image-233" src="http://www.frank-d.info/wp-content/uploads/2015/09/First-JFET-PCB viagra 50 oder 100.jpg” alt=”First JFET PCB” width=”281″ height=”500″ />

First JFET PCB (theoretically 36 at a time)

This was a pretty good choice for a first etched PCB, I went through a bunch of layout iterations for each module that would be duplicated over the board, and I finally got something that I liked — the trace layout looked better to me than some of the other options and it was efficient in terms in space usage from left to right. I couldn’t fit a 5th row on the PCB without significantly reducing how many columns I had. I intended on using PCB terminals from Radio Shack (hence the 0.3″ spacing next to the resistors), but they were too bulky so I just soldered some Male-Male jumper wire to hook into the Arduino and the 8-way relay boards I ordered before I decided to start making PCBs. I’ll probably wind up integrating the relay board onto the JFET tester with an ADC and a header to connect directly to the Arduino. At least making PCBs is a cheap hobby, and I’ve always wanted to make SO many PCBs — I’ve always resorted to wiring on standard perfboard with thin wire and a decent amount of solder to work as ‘traces’ for audio amplifiers. PCBs would make things SO much easier — if only I had a small CNC mill to drill all the holes for me!

JFET DUT Cell Evolution -- From Really Bad to Kinda Bad!

JFET DUT Cell Evolution — From Really Bad to Kinda Bad!

 

As you can see, each DUT Cell has gotten smaller with time. The last one got slightly larger to accommodate the RS PCB Terminals, but they’d need even more space to properly fit. They hit the resistor on the cell it’s in and on the one before it.. then there’s little clearance even between the terminals so it’d be hard to insert wires.

I actually picked up an AVR ATMega2560 based board cheap at MicroCenter. I’ve been using AVRs forever, the Arduino IDE just makes things a little easier  in some respects, even if it is a bit more limiting than I’d like. I’m used to using Atmel’s stuff, I’ve been using AVRs since the first ATMegas came out and there was a long lead time on the 16MHz variants, so at least I’m fairly familiar with them and their inner workings. I couldn’t resist buying the ATMega2560 board as it has *16* ADC inputs without using an external multiplexer or ADC. I have a few ADCs laying around, but the only one I could find is a TLC1543IN which wouldn’t work with the Arduino Due without a level shifter as this particular model of the 1543 (IN) is a 5v part, so it would blow up the Due’s 3.3v IO without bi-directional level shifters which I don’t have.. nor do I have signal MOSFETs, and IRF510s in a TO-220 would look ridiculous even in the interim. 🙂

I’ve only physically populated a single row, and I used 1% metal film resistors (again from Radio Shack since they’re right there and I don’t have to wait for things even if I pay through the nose and out the other side of it).  Clearly I’m not an electronics engineer, and my circuit design is probably poor overall for some reason, but the JFETs will (hopefully) not oscillate and we’re only testing two parameters so it should suffice. I measured the resistors to make sure I was reading the bands correctly (it’s been a while and I don’t have a magnifying glass — and damn they’re harder to read than I remember), and my little Fluke thought they were all within +/- 1%. I didn’t want reading variations with 5% resistors.

The process is the same as before. The relays are flipped to measure IDSS or Vpp, and we use a single pin to flip the relays. We’ve just scaled it up some by taking it off of a breadboard. You can see the PCB I printed this time only does 36 FETs at a time. I was trying to minimize the area outside of the center of the board and these are just prototypes so there was no reason to not do so.

Speaking of, I have design decisions to make for my prototypes — either use ATTiny828s that have 4 ADCs and mux them out to 28 for a mere $2.24 each (in TQFP from DigiKey) and put them on board (say with 112 JFETs on a larger board) with serial uplinks or to a control processor either on or off the board. With only 512B of RAM they’d need a separate processor to offload readings as quickly as possible. At least it’s cheaper than a halfway decent ADC and leaves me room to update their firmware and possibly do things a bit differently.

Here’s an example of *90* JFETs in the same board space (4.5″x6.375″), up from 36. They’re packed in tight, but there’s enough clearance everywhere. This one uses 2 pin male headers for each JFET.. routing them to a central place for a ribbon cable would be nice, but would require a two sided layout which I’m not quite ready for yet..

90 JFETs on a 28 in^2 board

90 JFETs on a 28 in^2 board

So I’m going to wire the 12 JFETs up to a couple 8-relay boards and see what happens. Hopefully I didn’t screw up the circuit design from my breadboard layout and there’s nothing seriously wrong with the design..

Part 3 incoming, it’s either going to detail a massive failure and/or another upgrade.. hooray?

 

HP ProLiant DL580 G5 — GOOD LORD HOW LOUD YOU ARE, Also: How to quiet down a DL580 G5

So these servers I got are insanely loud, and I can’t stress insanely enough. The fans don’t seem to spin down to any reasonable level even when nothing is stressed and the system as drawing a “paltry” 650w.

So since there’s no direct control of the fans, at least so far in my limited testing with FreeBSD which I’m unfamiliar with anyhow I decided to quiet things down the hardware way. I took each of the 6 120mmx120mmx38mm fan cages out with *65dB* fans rated at 150CFM and cut the power cables to the proprietary connector. There was no way to get a standard width fan in here easily, so I decided to try running each pair in series.

That didn’t go so well. The fans would spin up a bit and then spin all the way down, the server thought they were bad. 6 volts was not enough to keep them going.. so I decided to cheat another way. I cut the power wires to some of the remaining 4 and wired a few diodes in series (5 of the 6 fans have 2 diodes, one has 3). That should give me some voltage drop from the forward bias of the diodes, and it did! My system went from absurdly loud to manageable.

For the other server I’ll be trying 4 diodes in series to try to get a bit more Vdrop and a bit more manageable noise. So far, so good. The 1.5amp diodes aren’t quite enough for my 150CFM Deltas and managed to burn out. 4x 3 amp barrel diodes fit perfectly in the little cavity in the fan, but I don’t have any pictures to show of that at the moment unfortunately.

 

 

3 1.5amp Rectifier Diodes, Twisted Together

3 1.5amp Rectifier Diodes, Twisted Together

Step 1:

Twist the diodes together, anode to cathode (note the silver band), this will get us some voltage drop.

3 1.5amp Rectifier Diodes, Soldered

3 1.5amp Rectifier Diodes, Soldered

Step 2:

Solder these connections and clip the parts we just soldered, we just need the two ends. This step is basically the same for 4 diodes, you just cut one more twisted set.

Fan and cage separated

Fan and cage separated

Step 3:

If your fan has a cage, disassemble the fan from the cage. Mine had plastic push pins much like most cars do, after that it slipped right out as I spread it apart to take the custom connector out.

Diodes Placed on Fan, Tinned

Diodes Placed on Fan, Tinned

Step 4:

Place the diodes on the fan, you can use some super glue to hold them in the cavity if there is a cavity. Otherwise place them somewhere convenient. Tin the anode/cathode of the diode(s) and cut the main power wire to the fan. Tin those wires.

Diodes Wired To Fan

Diodes Wired To Fan

Step 5:

Solder the power wires. The incoming wire will be wired to the cathode, or to the diode with the band furthest away from the connection.

Assembled Fan

Assembled Fan

Step 6:

You should probably have used shrink wrap in Step 5 (doh!), use some electric tape to make sure the exposed power does not hit ground and short out. (Yes, I had this problem, even with the electric tape, and I had to do horrible things to get the fan going again since it uses an uncommon connector that I couldn’t just replace)

Rearranging The Intranet of Things Part II

I’m sure there will be a lot more posts like this to come. I had formerly moved the edge router to the ‘closet’ (aka the garage, right next to the cable modem and 3560-24PS sitting there) and added another router there to have a routed gig port into my ‘office’ (aka my bedroom with a couple desks).

Today I replaced both routers with a single 7206VXR with an NPE-G1. I had it all configured and everything should’ve worked off the bat, but it didn’t — not exactly, anyway. The routing was perfect, the NAT was great. But I only have a VAM card which doesn’t work with 15.x (only VAM2 cards work with new code), and I didn’t want it doing VPN in software.

So I decided to keep the old WAN router as VPN-only duty. I briefly considered using a 1760 with a VPN module (I have a few), but when I finally get to having decent internet speeds it would choke. The 3825 has an EPII+ card on top of the onboard hardware engine, so it should at the least have no issue keeping up with my internet connection with weak Triple-DES. The only issue is when I went to forward UDP 4500 from the edge router to the VPN router I got:

% Port 4500 is being used by system

I was able to successfully forward ports UDP 500 and ESP, but here I got stumped. I verified there was no crypto config, I tried clearing crypto stuff, I tried disabling software crypto — all with no luck. Googling didn’t give me much to go on, but I finally ran into something showing this error as an IOS-XE bug for 15.2(4)S2 –and I was running 15.2(4)S3 (pure IOS, but basically the same), so being out of options and ideas I decided to just install 15.2(4)M7 and Voila! Problem solved!

Two routers replaced with — two routers, maybe that doesn’t sound very good, but it will allow me to do more at the edge with more ports available directly on the router instead of playing with switches and VLANs/VRFs.

And in case you want to see how my network is physically wired — and this is somewhat simplified, here you are!

Network Diagram

Simplified Network Diagram – 01/01/15

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