Part of my real job is traffic counts, and I've been working on some permanent traffic counter setups.  The counters that we are using have an RS-232 interface, although in certain situations, an RS-485 connection must be used.

They don't make computers with RS-485 connectors on them (anymore).  So I've purchased an adapter, and then a coworker purchased another (more expensive) adapter.  The differences are interesting.

Adapter #1

Adapter #1 is an inexpensive $10 on Amazon (affiliate link). I'm not going to post an image of the inside, but there are 4 chips:

  1. an ME7660C Charge Pump (converts +5V to -5V)
  2. A 4093 Schmidt Trigger
  3. Two SP485EE RS-485 Interface chips

The reason for two RS-485 Interface ICs is because RS-485 is full-duplex, so my guess (without tracing the circuit board) is that one chip handles the positive RX/TX and the other handles the negative RX/TX.

Adapter #2

Adapter #2 is a far more expensive converter (it's $80 on Amazon, affiliate link). Similar to above, I'm not going to post an image of the inside, but it also has 4 chips... some similar, some not so much:

  1. 7660C Charge Pump
  2. MC14093 Schmidt Trigger
  3. SP3220 RS-232 Transciever
  4. SP485EEW Full Duplex RS-485 Interface

This particular adapter was recommended by the manufacturer of the traffic counters we are using, and my thought is that it has to do with the fact that it has a full-duplex interface.  I looked on Digikey to see if they have both types of chips, and they only stock the half duplex chip (for less than a dollar per chip).

I was so far not able to get either of these to work with the traffic counter, although I'm willing to bet that in both cases, it has to do with something that isn't the device (my wiring or needing to use a null modem adapter).

-73-


Category: Electronics

It's not really a secret that I love messing with Raspberry Pis - I have one (a first generation Raspberry PI) that acts as a VPN server and a temperature controller for my homebrew beer keezer, I have one (a third generation Raspberry Pi) that acts as a streaming media server, I'm preparing one (a 0W) for a homebrew beer fermentation chamber, and I have a few more 0s and 0Ws for different uses. That being said, I've started to customize my own prep routine for getting a new Pi Zero W (and this is adaptable) running.

Card Setup

  1. Image latest OS onto card: Use Etcher (from etcher.io)
  2. Boot once (this fixes a few things, most notably the SD card size)
  3. Setup as Ethernet Gadget (thanks Adafruit!)
    1. Card /boot/config.txt -> add dtoverlay=dwc2
    2. Card /boot/cmdline.txt -> after rootwait add modules-load=dwc2,g_ether
  4. Enable SSH: add file 'ssh' (no ext) in /boot/
    1. Alternative: sudo raspi-config - interfacing options - SSH - Yes
  5.  Add wifi info:
    1. Card /boot/wpa_supplicant.conf
    2. Should look like:
network={
 ssid="YOUR_SSID"
 psk="YOUR_PASSWORD"
 key_mgmt=WPA-PSK
 }

Device - after boot

  1. Connect with PuTTY to raspberrypi.local
  2. Change password: passwd
  3. Update host information in /etc/hosts and /etc/hostname
  4. Reboot to force update to AVAHI (mDNS): sudo reboot
  5. Update software: sudo apt-get update then sudo apt-get upgrade
  6. OPTIONAL: Install python pip: sudo apt-get install python-pip

Notes:

There's usually some easier ways to do these things, this is my way. As per usual, there's at least six ways to skin the cat and at least four of them are correct.

The case is from Thingiverse.


Category: Raspberry Pi

Backstory: I purchased some 24v pumps that I use in homebrewing beer.  Lacking any good option for a 24v DC output, I grabbed a doorbell thermometer at the hardware store and rigged it up in a single-gang box (don't try this at home, kids!).

For reasons likely involving moving boiling wort through one of these for 15 minutes before shutting off the heat (boiling wort is an effective sanitizer), I blew two transformers before looking into things.

The ultimate end of this is that I've decided to stop using the cheap pumps and am going to purchase a decent pump.

-73-


Category: Electronics

Many years ago, I purchased a wine cooler on clearance at the local grocery store. I soon found why it was on clearance: it's default set temperature was in the 30s (Fahrenheit) and it didn't remember the set temperature after a power loss.

Wine cooler

So the wine cooler sat for many years, unused. Until now.

I don't drink wine, but I brew beer. In brewing, yeast like certain temperatures - mid-60s to low 70s for ales, and mid-50s for lagers.  While I normally brew ales, every so often I like a nice lager (few things beat a nice Marzen in the fall, or a nice Bock in the spring).

Top side of controller board

Bottom of controller board. Note the blank line between the high and low voltage sides of the the supply.

After taking apart the cooler, I realized it's basically a switching 120V - 12V power supply with a controller for a negative temperature coefficient temperature sensor.  Without anything connected to the NTC pin, nothing happens. However, if I short the NTC pin to ground, it turns on the chiller. As seen below in the headache-inducing video, the device works.

This is the first part - the second part will be a controller. And at some point, I'll have to figure out if I can actually use this to keep 5 gallons of beer cold.

73

Update: removed the smaller (cold side) heat sink to get the part number.  It is a TEC1-12706.

At a hot side temperature of 25ºC:
Qmax (Watts) 50
Delta Tmax (ºC) 66
Imax (Amps) 6.4
Vmax (Volts) 14.4
Module Resistance (Ohms) 1.98


Category: Electronics

Somehow I ended up finding a Tessel GPS on Seeed Studio for $20 (it's not $20 currently, but maybe someday soon). The Tessel GPS is really a Maestro A2235-H GPS chip on a semi-convenient breakout board.

Tessel GPS Module

I want to use it with a Raspberry Pi Zero-W.

The problem is that the GPS output appears to be a newer type of data called OSP.  It's not easy to read, and I didn't find any pre-built libraries that decode it.  If one slows the baud rate down, the output is in NMEA, which is standard and free libraries exist.

Raspberry Pi-0W OS Setup

I'm assuming the use of Raspbian here.

Recommended first-time setup courtesy of Adafruit.

A few things need to happen on the Pi-0W: turning off the serial console.

  1. $sudo raspi-config
  2. Option 5: Interfacing Options
  3. P6: Serial
    1. No, you don't want the shell accessible over serial
    2. Yes, you want serial port hardware to be enabled
  4. Finish
  5. $sudo shutdown -h now

The last command is shutdown because at this point, I'm assuming the hardware is not plugged in.

Raspberry Pi-0W Hardware Setup

The Tessel GPS breakout has the TX and RX inverted (depending on how you look at it).  Pi-0W pin 1 to the Tessel GPS 3V3 power, pin 6 to the Tessel GPS ground, pin 8 to the Tessel GPS TX, and pin 10 to the Tessel GPS RX.

Tessel GPS Hookup Diagram

Live-ish Hookup Diagram

Reading From The Device

When the device is first powered on, any serial connection prints gibberish because the GPS strings are in hex.  To change that, one must send a string of bytes to the GPS device.  I've prepared a quick python script to do just that:

Once this script is run, any serial connection can be made to the GPS device, such as:

$sudo minicom -b 9600 -o -D /dev/serial0

Or with python or another language.


Category: Raspberry Pi

I've had a mobile radio installed in my S-10 for years.  However, for the longest time, it was only half right.  I did the correct thing and not use my truck's accessory outlet wiring. I haven't figured out for the life of me how General Motors claims you can put 20A on a 20 gauge wire - 20A for any sustained period of time on such a small wire is a significant fire hazard.

This is the wrong way to do this.

Initially, I took the quick, easy, and cheap way out by sandwiching the radio power lead in the battery post. However, I ran into a problem a few times in the mornings where my truck wouldn't start.  I found that the positive power lead was not staying tight. I eventually removed the power lead because I like to be able to drive my truck. And besides, no power was getting to the radio, either!

Enter the correct solution.

Better Battery Bolts

The correct solution is $5 each (and two are needed). Not really expensive.

The correct solution

This works better for two ways - the first is that the new battery bolts are longer ensuring a more reliable connection between the battery and the cables.  The second is that the wires are not between the battery and the main vehicle power.  I might be over-stating that benefit, though, as I don't think the power lead lugs were causing any significant power drop.

73 de KE8P


Category: Equipment
Tags:

At the Milford Hamfest, Debco Electronics was selling off grab bags.  I bought two (and I'm calling them Junk Box Fillers)... of note:

  • 74155 ICs - 2 line to 4 line decoder/demultiplexers
  • LM613 Dual Op-Amp and Dual Comparator and Adjustable Voltage Reference
  • M5229P Seven Element Graphic EQs
  • 15 trimmer resistors
  • 9 variable resistors (8 appear to be the same)
  • Some 2N4861 JFETs
  • Some IRL530 MOSFFETs
  • Some other bipolar transistors
  • Some touch tone decoders (one not on a circuit board, at least one on a circuit board)
  • Some display boards

 

Pictures:

ICs, trimmers, variable resistors

ICs, trimmers, variable resistors

Stuff that I don't know what it is

Stuff that I don't know what it is

Displays!

Displays!

Jacks, connectors

Jacks, connectors


Category: Electronics
Tags:

My work has taken me down the road of using Raspberry Pis as data collection devices.  This means I need to power a Raspberry Pi in the field.  I've had trouble finding a reasonably-priced 12V to 5V USB adapter that I could easily and safely fit into a box with a RPi.  So I designed one in KiCAD and built it.  The design is on my work github account.

I'm ultimately designing something that will connect to a battery, and batteries can explode if mistreated.  Testing is critical, as is circuit protection (the fuse).  I'm envisioning this to be in a box on the top of a pole with a camera, so the lead going from the battery (which will likely be on the ground) will be fused in case the wire gets cut.  This is critical for the same reason it is necessary in a car - to protect the battery from short circuiting should something happen.

Empty PCB

Empty PCB

Test fit components at the office.

Test fit components at the office.

In putting these together at home, I tested these in every way I could think of, and assembly and testing went something like this:

  1. Solder SMD C2 and R1
    1. Test resistance from 7805 output to LED positive solder hole, should be 330 ohm (I used 330 ohm resistors instead of 310, since I don't happen to have any 310 ohm).
    2. Test continuity from 7805 output to ground via connected to C2. Should show no continuity.
  2. Solder USB connectors and C1
    1. Test capacitance from 7805 input to to ground via near C1. Should show a reading (mine all showed around 1000 uF, which is high, but my understanding is that multimeters are notoriously bad at capacitance)
  3. Add input headers, fuse holder, and LED
    1. Test continuity between inputs - should immediately beep, and then drop to no continuity after capacitors charge
    2. Apply voltage, LED should light, all magic smoke should remain contained in devices
    3. Test voltage from 12V- to 7805 output - should be 5.0v (mine showed something like 5.007v)

The one thing I was unable to test was the actual USB output voltages, but it seems to me that they should be okay.

IT LIVES!!!

IT LIVES!!! This is one of 5 I built.

I have five blank PCBs left for additional builds should I need it, although I'd have to have work buy more components.  Maybe I could get some larger 7805s that would fit the ground pad...

-73-


Category: Electronics

In terms of success, this ranks up pretty high.  I wheeled-and-dealed on everything, and I feel like I made out like a bandit!  I didn't stay very long at Hamvention - I arrived around 8:30 AM and I was gone by around 1:30 PM.

Astron VS-20 Power Supply

It works. I needed a power supply for my bench, and everything new was either adjustable (but not powerful and expensive) or powerful and expensive.  This is better than I thought I'd end up with.

VS-20M Power Supply

VS-20M Power Supply

RF Millivolt Meter

This is one of those pieces of equipment that I never thought I'd have because they're fairly specialized.  I saw a few, and after finding the power supply, I looked for one I had already found.  I found this one (with the probe, not pictured) instead.

Millivolt Meter

Millivolt Meter

Percent Explosive Meter

I'm surprised someone else didn't get this first!  I couldn't resist it.  This is going to find a place in my basement near a blinking red light.  I'm not sure what it will otherwise be connected to (if anything other than a random/semirandom/not-random time controller), though.

Percent Explosive!!!

Percent Explosive!!!

Anderson Powerpoles

I'm standardizing on these expensive AF things.  I needed some.

Powerpoles.

Powerpoles.

Hands On Radio Experiments books

After reading N0AX's articles in the last few QSTs, the method of teaching has really grown on me.  When I saw experiment #161 in the June 2016 QST, which referred back to a common emitter amplifier, I not only read with interest but also decided to attempt the experiment.  I started looking for all of the experiments and saw that the ARRL prints them in a book.  I found the books at W0TOK books and wheeled-and-dealed to both for $30.  DEAL!

2016-05-21 11.48.56

Not from Hamvention: Etherkit Si5351 Breakout

I ordered an Si5351 Breakout Board from Jason/Etherkit a few days before Hamvention and got it on Friday after I returned from Hamvention.  I got one on the kickstarter campaign, but SEE THE UPDATE BELOW! but for some reason it refuses to work despite some troubleshooting.  My guess is that I damaged the chip somehow since I THINK (operative word!) that the two MOSFETs work correctly but my Bus Pirate won't show an available address .  For whatever idiotic reason, each time I get something from Etherkit, I try to hot-air solder it, and it's all been without the right stuff (either without a proper hot air rework station or solder paste).  I've been set straight thanks to the Twitterverse, and someday will replace damn near every component on my CRX1 and get it to work properly.  And I will always remember the sign in my dad's auto shop: "Don't be a fool, use the right tool!"... I'll also remember Dr. Miller (photography teacher at my high school): "Do not use any equipment for which you have not been trained" (in other words, make sure I know how to set the jumpers before setting power!).

EDIT: I typed all this before testing the new breakout board.  The new breakout board was throwing errors, and I found that the new oscillator pulls more current than the Bus Pirate seems to want to provide.  After finding this, nothing could be found with the I2C search.  I looked back on this blog and found "the CLK pin on the Bus Pirate gets connected to the SCL pin on the demo board and the MOSI pin on the Bus Pirate gets connected to the SDA pin on the demo board."  I now have two functioning breakout boards! 🙂

Etherkit Si5351 Breakout

Etherkit Si5351 Breakout

That's it! 73!


Category: General Stuff
Maybe it'll be a good day!

Maybe it'll be a good day! From WHIO TV 5/16/16

I'm going to Hamvention on Friday.  My shopping list consists of a handful of needs:

  • A power supply (preferably a linear supply capable of >=20 amps continuous, but I'd go down to 10 amps switching if needbe)
  • Powerpoles
  • An NMO mount or two
  • Variable resistors: 500 ohm, 50k, probably a few in between
  • Something to make a 100Mhz or 125Mhz oscillator
  • Probably a few other parts
  • Some MOSFETS... particularly an MPF-102 for this

I'll probably come home with other stuff too...

-73-


Category: General Stuff
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