Electrical Engineering V3

[Chryseus]

Someone asked me to design them a mono 3kHz high and low pass audio filter so I gave it a shot.
[t]http://i.imgur.com/lVJLm8v.png[/t]

Topology is a sallen-key 3rd order filter using a single op-amp with a chebyshev 0.5dB response.
I used the [b]very handy[/b] design tables from [url]http://www.glensstuff.com/activefilterdesign/activefilterdesign.htm[/url] along with some manual tweaking to get it reasonably matched for high and low pass.

[Papkee]

A question to the people who might have the answer:

I've been looking for an RF Amplifier circuit for the 150mhz band. I was thinking about 5W~10W power, and I can find nothing about amps in this frequency range for some reason. Is it just complicated to do one for this range or do people just not use the higher VHF frequencies that much for hobby radio?

[Ddrl46]

[QUOTE=papkee;47291975]A question to the people who might have the answer:

I've been looking for an RF Amplifier circuit for the 150mhz band. I was thinking about 5W~10W power, and I can find nothing about amps in this frequency range for some reason. Is it just complicated to do one for this range or do people just not use the higher VHF frequencies that much for hobby radio?[/QUOTE]

Maybe this? Searching for "2 meter rf power amplifier" gives a bit more results.
[url]http://www.m0ukd.com/homebrew/2n6084-144mhz-fm-power-amplifier/[/url]

Plenty of people up at the higher frequencies, even into the multi GHz range.

[Papkee]

This thing is perfect for what I need.

Too bad it doesn't exist anywhere and the few places that have it want almost $40 for one.

[url]http://www.qsl.net/sv1bsx/mhw612/mhw612.html[/url]

[LoneWolf_Recon]

Motorola never seems to have a good archive of their datasheets. Here's an alternative on a more widespread, and well documented, [URL="http://pdf1.alldatasheet.com/datasheet-pdf/view/1101/MITSUBISHI/M57737.html"]Mitsubishi M57737[/URL]. Its only good for CW & FM modes of transmission on the 2m band (As its a Class-C amp), but still fairly common place.

[URL="http://bmarc.org/techcorner/simple-30w-class-c-pa-unit-2m-use"]Here's[/URL] an example PA setup like yours that uses it.

[URL="http://www.w6pql.com/2_meter_80w_all_mode_amplifier.htm"]Here's[/URL] another setup like it that supports both FM/CW & AM/SSB, using a [URL="http://www.rfparts.com/fileuploader/download/download/?d=0&file=custom%2Fupload%2FFile-1362185227.pdf"]Toshiba S-AV36[/URL].

The [URL="http://www.arrad38.fr/datasheet/S-AV17.pdf"]Toshiba S-AV17[/URL] is much more widespread and documented, thus I'd recommend that much more than the other two.

The $30-$50 cost for it, or any standalone VHF module like it, is kinda inescapable. They're rather complex amplifiers.

Now of course, if you're using any other mode i.e. AM/SSB/etc (Which is rather rare on 2m), you'll need a linear amp (Class A, Class AB).

[editline]10th March 2015[/editline]

Seems to be that the Icom SC1091 is the direct/pin-compatible replacement module for the SAV17, thus look into that module as well.

[Chryseus]

Most amplifiers above 50MHz or so are made with discrete transistors only, while ICs are available up to a few GHz they are costly and usually restricted to lower power.
It isn't that difficult to build your own RF amplifier, 150MHz isn't all that high so you don't need to be that careful with physical layout although you do need to take things like miller capacitance into consideration, something like a common-base configuration or a cascode will work very well.

[Papkee]

[QUOTE=Chryseus;47296077]Most amplifiers above 50MHz or so are made with discrete transistors only, while ICs are available up to a few GHz they are costly and usually restricted to lower power.
It isn't that difficult to build your own RF amplifier, 150MHz isn't all that high so you don't need to be that careful with physical layout although you do need to take things like miller capacitance into consideration, something like a common-base configuration or a cascode will work very well.[/QUOTE]

Barring that I do not understand the second half of what you just said, it's hard to find schematics or circuits that give you equations or things that tell you "for x frequency, use this formula." Most of them just tell you what will work for the specific application they are designed for.

Any good learning resources? I've been using the ARRL site and I know just enough to know that I don't know anything about anything.

[LoneWolf_Recon]

[QUOTE=papkee;47296409]Barring that I do not understand the second half of what you just said, it's hard to find schematics or circuits that give you equations or things that tell you "for x frequency, use this formula." Most of them just tell you what will work for the specific application they are designed for.

Any good learning resources? I've been using the ARRL site and I know just enough to know that I don't know anything about anything.[/QUOTE]

That's a very loaded question, alot of it is heavily drawn upon amplifier basics and a working knowledge of transistors (Either BJTs or FETs). I would start small to understand amplifier basics in audio frequencies and then graduate up to RF ([URL="http://www.electronics-tutorials.ws/amplifier/amp_1.html"]Here's[/URL] a great resource to practice on, also check OP). Once you get into HF/VHF/beyond parasitic/miller capacitance becomes more of an issue affecting frequency response, etc. On top of that, I'd also look into filters (Low/High Pass & Pi Filters).

As for the higher tier (RF PA design, etc) stuff, I found this [URL="http://www.qsl.net/va3iul/"]site[/URL] to be pretty helpful.

[Goz3rr]

We got what appear to be HC-05 to use with our robotics project and I'm trying to get into AT mode to change it's name since having 20 HC-05 devices found is a bit tricky. I've used this arduino script:

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

void setup() {
  Serial.begin(9600);

  pinMode(9, OUTPUT);
  digitalWrite(9, HIGH);

  Serial.println("Enter AT commands:");
  mySerial.begin(38400);
}

void loop() {
  if(mySerial.available()) {
    Serial.write(mySerial.read());
  }

  if(Serial.available()) {
    mySerial.write(Serial.read());
  }
}

TX/RX pins are connected to 10,11 as in code, KEY pin to 9 (HIGH) and the LED blinks like it should in configuration mode, but when i send the AT command in the serial monitor i get "O£†…" back instead of "OK". However, sending "AT+NAME=TEST_THING" will actually change the name, but when running "AT+NAME?" it'll return garbage. Honestly I'm glad we can change the name but I would like to know what the hell could be causing this

[Leestons]

I love how much my knowledge of electronics has grown over the last couple of years. This time three years ago I thought a 555 timer was an actual timer, like what you would find in your kitchen or something with a 7 segment display. Capacitors were just the round things that stick up on a circuit board, and I didn't even know they were called that. I could count the amount of solder joints I had made on one hand.

Now I know a lot about components, I can design circuits, soldering doesn't worry me anymore and I actually enjoy it. I understand things when people talk about current, ohms law etc. I'm still a total beginner and I know almost nothing compared to some of you here but I'm slowly getting there. I used to regret taking product design as a GCSE in school instead of electronics, not knowing that I would develop an interest a few years later, but now I feel I know most of the things I'd learn there so it doesn't bother me as much.

[LoneWolf_Recon]

Using the software serial terminals is rather unstable, in my experience, especially at higher bauds. See if its possible to lower your baud speed to say 9600 or 4800 to get a stable output. Thus I think your arduino can send the data at 38400 baud but not receive very well.

[Goz3rr]

[QUOTE=LoneWolf_Recon;47301870]Using the software serial terminals is rather unstable, in my experience, especially at higher bauds. See if its possible to lower your baud speed to say 9600 or 4800 to get a stable output. Thus I think your arduino can send the data at 38400 baud but not receive very well.[/QUOTE]

The connection between the Arduino and the Terminal should be 9600 and between the Arduino and the HC-05 is 38400 baud, I got that value from datasheets and other people who are using the exact same code on their arduino where it seems to work. I don't think I can change that value.

Is there a difference between using the default pin 0 and 1 serial ports and a SoftwareSerial?

[LoneWolf_Recon]

[QUOTE=Goz3rr;47302778]The connection between the Arduino and the Terminal should be 9600 and between the Arduino and the HC-05 is 38400 baud, I got that value from datasheets and other people who are using the exact same code on their arduino where it seems to work. I don't think I can change that value.

Is there a difference between using the default pin 0 and 1 serial ports and a SoftwareSerial?[/QUOTE]

Yes, SoftwareSerial is essentially interrupt-based bit banging which can be accurate depending upon how free the CPU is. Pins 0/1 are tied directly to the arduino's hardware UART system which is independent of the CPU and thus not affected by heavy computational loads.

According to the datasheet you could send out AT+UART=9600,0,0 to set the HC-05's baudrate to 9600, 1 stop bit no parity. By default it should bet set to that, you can check that by sending AT+UART?.

Or even better, disable your uart on your arduino, and tie the HC-05 directly to pins 0/1 respectively and thus talk directly to the HC-05 via your terminal.

[Goz3rr]

[QUOTE=LoneWolf_Recon;47302907]Yes, SoftwareSerial is essentially interrupt-based bit banging which can be accurate depending upon how free the CPU is. Pins 0/1 are tied directly to the arduino's hardware UART system which is independent of the CPU and thus not affected by heavy computational loads.

According to the datasheet you could send out AT+UART=9600,0,0 to set the HC-05's baudrate to 9600, 1 stop bit no parity. By default it should bet set to that, you can check that by sending AT+UART?.

Or even better, disable your uart on your arduino, and tie the HC-05 directly to pins 0/1 respectively and thus talk directly to the HC-05 via your terminal.[/QUOTE]

I realized afterwards that if I use pin 0 and 1 I can no longer communicate with the PC terminal over USB and would need a second arduino/usb to ttl for that, the AT+UART only affects the bluetooth baud rate I believe, not the rate in configuration mode. Besides that if that was the issue wouldn't I be unable to properly write data to it? The problem is receiving data so it's impossible to check the value of AT+UART? because it just returns garbage

[editline]11th March 2015[/editline]

So after looking into this a bit more, I found an issue on the github describing my exact problems, transmitting works fine at 38400 baud but receiving is mangled garbage. Turns out it was fixed in a commit 6 days ago and patched in 1.6.1

i'm on 1.6.0

i ignored the update message thing this morning

[b]kill me now[/b]

[Chryseus]

[media]http://www.youtube.com/watch?v=tHbtp4Hes-M[/media]

I'm happy it's working now, after I screwed up twice putting the wrong value components in.

[Papkee]

Pretty tubes.

So I've got more RF questions - I really like that Toshiba 30w unit that was posted above - [URL="http://bmarc.org/techcorner/simple-30w-class-c-pa-unit-2m-use"]the example circuit[/URL] is simple and I understand the basics of the filtering; I just need to modify the lowpass for my frequency.

One thing I'm not too sure about - the T/R switch. The way I understand it is that you don't want to be running your received signals through the amplifier, so the relay switches it off and bypasses the amp sending the RF directly to the receiver. Is that a correct assumption?

My application is this: I'm going to be putting that nifty VHF radio module, along with an atmega of some kind and the amplifier into one of those extruded aluminum boxes from ebay. It'll be my new mobile radio for my car. Is there anything to consider for vehicle use besides good power regulation and filtering?

[LoneWolf_Recon]

That sums it up, it simply bypasses it so you can directly receive the signal. Proper regulation and filter are a must, and see if its possible to ground that box (with a short-as-possible ground lead) to the chassis along with potentially putting a choke on the power line feeding to your unit.

You may want to consider finding a more direct connection to your car's electrical system as most cigarette lighter sockets are fused, considering you'll only be using about 50W-60W (taking into account amplifier inefficiencies, misc) you should be fine through your cigarette lighter socket but I would check nonetheless.

I didn't notice previously, but that 30W circuit allows Toshiba SAV17s as a drop in replacement.

I'm curious, what are you planning to use the atmega for?

[nikomo]

It's scientifically proven that any circuit will magically be better if you add an ATMega or PIC to it.

[Cakebatyr]

Probably to perform APRS.

[Papkee]

Actually the VHF module needs a UART connection to set the frequency, so I figured I'd just use it for controlling the module as well as adding an LCD and some buttons for control.

[pentium]

[quote="Mike Douglas of AltairClone.com"]I'm down to six Clones left out of the last run of 50, and I'm not sure yet whether I'm going to do another run. So even though I sound like a used car salesman right now, I wouldn't wait too long :)
[/quote]

...ONE DAY before my paycheck.
[url]http://altairclone.com/ordering.htm[/url]

[quote]Altair 8800 Clone Computer
(assembled)
$621

[highlight]out of stock[/highlight][/quote]

Well there goes my next project before I could even start it.

[Cakebatyr]

[QUOTE=papkee;47308160]Actually the VHF module needs a UART connection to set the frequency, so I figured I'd just use it for controlling the module as well as adding an LCD and some buttons for control.[/QUOTE]

You could toss in an ATtiny84 (or 85 if you really want) if you just need to be able to select frequency. A rotary encoder or two buttons and bam, full frequency select.

[Papkee]

[QUOTE=Cakebatyr;47310620]You could toss in an ATtiny84 (or 85 if you really want) if you just need to be able to select frequency. A rotary encoder or two buttons and bam, full frequency select.[/QUOTE]

Yeah but I like LCDs far too much to not include one.

[editline]12th March 2015[/editline]

How exactly would I go about selecting inductors and capacitors for an RF lowpass filter? I know the values I need but I have no clue how to figure out voltage and current ratings - from what I understand RF necessarily have voltage or current, but there's my just enough knowledge thing again.

[Seiteki]

I can't post any pictures, but I can say I hate the engineers here and wish they'd get, and use, flight data before designing everything so I wouldn't have to go in later and add entire systems to fix their mistakes.

And then when the hardware is complete and correct per design and documentation, I wish they didn't blame my department for issues caused by their work or the software team's ineptitude.

Some days, I wish I didn't work in flight simulation at this level.

[Chryseus]

[QUOTE=papkee;47310961]Yeah but I like LCDs far too much to not include one.

[editline]12th March 2015[/editline]

How exactly would I go about selecting inductors and capacitors for an RF lowpass filter? I know the values I need but I have no clue how to figure out voltage and current ratings - from what I understand RF necessarily have voltage or current, but there's my just enough knowledge thing again.[/QUOTE]

Inductors at your frequency of interest can either be wound on ferrite or air core (air core still means you can wind it on something as long as it's not metallic or ferromagnetic), inductors of a larger radius generally have a higher Q, not too critical for passive filters, for power rating you don't need to really worry unless it's very thin wire.
Capacitors you pretty much need film, mica or single layer ceramic, multi-layer is a big no due to applied voltage changing capacitance.

For design remember to take tolerance into account, also the source and load impedance will effect the response a lot, I suggest using [url=http://www.omicron-lab.com/quickfil.html#5]this[/url] or [url=http://sim.okawa-denshi.jp/en/Fkeisan.htm]this[/url] to determine the best values.

[Koifish]

Hey.
I got my first ever Ardiuno and was wondering if you guys would have any basic tutorials or tips working these things?

I'm interested in making a small, playable piano using a bread box, buttons and speakers. thanks.

edit: Ardiuno Uno, sorry

[Papkee]

[QUOTE=SirDavid255;47312334]Hey.
I got my first ever Ardiuno and was wondering if you guys would have any basic tutorials or tips working these things?

I'm interested in making a small, playable piano using a bread box, buttons and speakers. thanks.[/QUOTE]

You're going to be limited primarily by your number of inputs. If you want more than 12 playable keys, you'll need to look into multiplexing unless you're using a bigger arduino like the mega.

It really depends on how much you already know, but the [URL="http://www.arduino.cc/"]arduino.cc[/URL] website has a lot of really good tutorials, and their forum has a lot of good, helpful information.

[Leestons]

Youtube has a lot of good tutorials too.

[woidoi]

blue seems to be the new green

[t]https://dl.dropboxusercontent.com/u/43645231/photos/electro/2015-03-13%2023.14.44.jpg[/t]

and color correction is something my camera has no fucking intention of doing :v:

[POLOPOZOZO]

Does anyone know stuff about rotary switches?
I'm looking for something with discrete stages but a really smooth action and a soft detent, like a left/right balancer on an amp or something
What am I trying to find here?