Author Topic: Oscilloscopes needed?  (Read 7872 times)

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Offline zerorisers

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Oscilloscopes needed?
« on: September 23, 2015, 01:32:09 pm »
Hey guys zerorisers here, I have been attempting to program an MSP430 using only Texas Instruments samples. But I have been wanting to make sure I had the pin-out of my comport correct. I am horrible at reading pin-outs and getting everything correct, it took me three tries and Im still not sure.(Massive ADD) is there any kind of measurements I can do to make sure I have the pin-out correct? or do I just have to connect everything up in hopes I have it correct?


(I own a multi-meter, ummmm... Yea that's the only piece of test equipment I own.)
 

Offline LA7SJA

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Re: Oscilloscopes needed?
« Reply #1 on: September 23, 2015, 02:47:45 pm »
Not to much information, I don't think anyone would even try to help you before they understand what you are trying to do with what hardware. I do not understand the term 'Texas Instruments samples', is this a sample board, chip or development board or?

Johan-Fredrik
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Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #2 on: September 23, 2015, 03:32:14 pm »
Not to much information, I don't think anyone would even try to help you before they understand what you are trying to do with what hardware. I do not understand the term 'Texas Instruments samples', is this a sample board, chip or development board or?

Johan-Fredrik

"Texas Instruments samples"  is a term for chips that TI will give out for free to students. MAX-232, SN60400, and TPS60400QDBVRQ1 are chipsI have ordered from TI in order to program the MSP430 off of a COM port. My main question is how do I make sure that I have the pin-out of the COM port correct, as the main port is just pin headers on the motherboard I have brought over to the RS-232 connector.
 

Offline Orange

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Re: Oscilloscopes needed?
« Reply #3 on: September 23, 2015, 03:36:02 pm »
Why do you post this in testequipment, with a silly Oscilloscopes title ?
 

Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #4 on: September 23, 2015, 03:40:30 pm »
Why do you post this in testequipment, with a silly Oscilloscopes title ?

To see wether or not I would need an oscilliscope to do this. I have software on my computer to pumpdata out of the COM port so I may be able to see the data output with an oscilliscope (if I had one) and was wondering if there was any way I could test this without one, or if there is a particular bandwidth oscilloscope that I may need.
 

Offline krivx

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Re: Oscilloscopes needed?
« Reply #5 on: September 23, 2015, 03:45:59 pm »
I find the best way to avoid wiring errors is to draw a diagram on paper.
 

Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #6 on: September 23, 2015, 03:54:54 pm »
I find the best way to avoid wiring errors is to draw a diagram on paper.
It is already put together and I have burned myself 5 different times trying to do so. (nothing to hold it still so i usually use my knees to hold stuff like my soldering iron.) I am hoping not to do that again.

I have had to make do a custom wiring job that I will take pictures of later today, as right now I am in school.
 

Offline Performa01

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Re: Oscilloscopes needed?
« Reply #7 on: September 23, 2015, 04:02:49 pm »
Pretty much any electronics project will benefit from an oscilloscope for analysis & debugging purposes.
As you're mentioning a COM port, a serial protocol analyzing function (for UART) would be helpful. Many scopes and all logic analyzers can do this. For scopes it's usually an option at additional cost. An USB logic analyzer would be the cheapest solution, and pretty handy for digital stuff anyway, but you might still want a scope on top of that, once you're starting real projects with the MSP430.
There are also mixed signal scopes (MSO) that combine analog and digital channels, hence can act as a substitute for a logic analyzer to a certain degree. But as I stated before, if a scope supports serial decoding, it will do it on the analog channels as well, so the mixed signal option isn't really necessary if you only want to check an UART or TWI bus every now and then.
 

Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #8 on: September 23, 2015, 04:05:33 pm »
Pretty much any electronics project will benefit from an oscilloscope for analysis & debugging purposes.
As you're mentioning a COM port, a serial protocol analyzing function (for UART) would be helpful. Many scopes and all logic analyzers can do this. For scopes it's usually an option at additional cost. An USB logic analyzer would be the cheapest solution, and pretty handy for digital stuff anyway, but you might still want a scope on top of that, once you're starting real projects with the MSP430.
There are also mixed signal scopes (MSO) that combine analog and digital channels, hence can act as a substitute for a logic analyzer to a certain degree. But as I stated before, if a scope supports serial decoding, it will do it on the analog channels as well, so the mixed signal option isn't really necessary if you only want to check an UART or TWI bus every now and then.

Alright well I guess I will start looking on craigslist, and hope I can find something under $50 to start with.
 

Offline Howardlong

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Re: Oscilloscopes needed?
« Reply #9 on: September 23, 2015, 04:10:44 pm »
I used to debug this kind of stuff with an LED+resistor, watching for a change in brightness when transmitting characters. A multimeter can be used too, measure the voltage and see if it dips when you continually transmit characters.

These days, yes, I'd use a scope, because it's set up and ready to go on the bench, but I developed and debugged far more complex things with just an LED and analogue multimeter for many years, the trick is learning for yourself what can be expected and achieved with such simple tools.
 

Offline Performa01

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Re: Oscilloscopes needed?
« Reply #10 on: September 23, 2015, 04:20:05 pm »
Yes, for just monitoring if _something_ is going on, you can probe the RXD/TXD lines with the DMM in ACV mode - provided, the meter has sufficient bandwidth, which would be a problem with cheap DMMs.
One more thing - do you try to interface the MCU directly to the COM port of a PC? I just want to make sure you are aware that the UART interface on the MCU is TTL, whereas the COM port on a PC is RS232. Even though the standard COM ports on a PC usually are TTL compatible to a certain degree, the voltage level will probably be too high for a MCU, especially if it runs on less than 5V rails. The usual solution would be an RS232 transceiver like MAX232 or one if its low voltage derivatives, but if you count on the TTL compatibility of the COM port, you would need at least some protection circuit to limit the voltage on the MCU port pins. Also serial ports on extension cards and USB to RS232 adaptors tend to _not_ have the before mentioned TTL compatibility.
 

Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #11 on: September 23, 2015, 04:29:49 pm »
Yes, for just monitoring if _something_ is going on, you can probe the RXD/TXD lines with the DMM in ACV mode - provided, the meter has sufficient bandwidth, which would be a problem with cheap DMMs.
One more thing - do you try to interface the MCU directly to the COM port of a PC? I just want to make sure you are aware that the UART interface on the MCU is TTL, whereas the COM port on a PC is RS232. Even though the standard COM ports on a PC usually are TTL compatible to a certain degree, the voltage level will probably be too high for a MCU, especially if it runs on less than 5V rails. The usual solution would be an RS232 transceiver like MAX232 or one if its low voltage derivatives, but if you count on the TTL compatibility of the COM port, you would need at least some protection circuit to limit the voltage on the MCU port pins. Also serial ports on extension cards and USB to RS232 adaptors tend to _not_ have the before mentioned TTL compatibility.

I will be using a MAX232 for this application (couldnt find it in a DIP format for some odd reason... no chip I try to get from TI seems to have any DIP format and is all surface mount with pins really close together.) so I want to check everything before I plug it in as it was a pain to put together. But I will try the LED method, and hope that works to check the few pins I need.
 

Offline LA7SJA

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Re: Oscilloscopes needed?
« Reply #12 on: September 23, 2015, 05:58:52 pm »
If you just want to monitor/check 3.3v/5V ttl "RS232" you could use this http://dangerousprototypes.com/docs/Bus_Pirate, mine came from http://www.seeedstudio.com/depot/Bus-Pirate-v36-universal-serial-interface-p-609.html and I was so happy with it that I got this http://www.seeedstudio.com/depot/Bus-Pirate-v36-acrylic-case-v1-DP6037-p-1229.html this was my main embedded debuging tool for a very long time.

Johan-Fredrik
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Offline jlmoon

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Re: Oscilloscopes needed?
« Reply #13 on: September 23, 2015, 06:21:45 pm »
Why do you post this in testequipment, with a silly Oscilloscopes title ?

"TestEquipment"?  I'm confused.  Last time I checked this guy posted in the 'Beginners' section.  Which he obviously is.   :-//
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Offline GreyWoolfe

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Re: Oscilloscopes needed?
« Reply #14 on: September 23, 2015, 06:58:21 pm »
Pretty much any electronics project will benefit from an oscilloscope for analysis & debugging purposes.
As you're mentioning a COM port, a serial protocol analyzing function (for UART) would be helpful. Many scopes and all logic analyzers can do this. For scopes it's usually an option at additional cost. An USB logic analyzer would be the cheapest solution, and pretty handy for digital stuff anyway, but you might still want a scope on top of that, once you're starting real projects with the MSP430.
There are also mixed signal scopes (MSO) that combine analog and digital channels, hence can act as a substitute for a logic analyzer to a certain degree. But as I stated before, if a scope supports serial decoding, it will do it on the analog channels as well, so the mixed signal option isn't really necessary if you only want to check an UART or TWI bus every now and then.

Alright well I guess I will start looking on craigslist, and hope I can find something under $50 to start with.

Not sure how many channels or how much bandwidth you need, but I got one of these to play with:
http://www.ebay.com/itm/New-Set-USB-Logic-Analyzer-Device-USB-Cable-24MHz-8CH-24MHz-for-ARM-FPGA-/291457642276?hash=item43dc3aaf24
It works with the Saleae software.
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Offline alsetalokin4017

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Re: Oscilloscopes needed?
« Reply #15 on: September 23, 2015, 07:42:13 pm »
Didn't the OP just ask for the pinout of the COM port? I think that it might take more than a few posts here for him to sort out the pinouts by probing with a multimeter, an LED or even an oscilloscope.....

Would it be out of place to suggest that he simply google "COM port pinout" and look at the images displayed?



But does his computer even have a proper serial port connector? Nowadays pretty much everything is done over USB, isn't it?

Somehow I doubt that working with SMDs on one's lap with a soldering iron between the knees is going to work out too well. And 50 dollars isn't going to buy much of an oscilloscope, when a pair of barely usable probes will cost 25 dollars or more.
The easiest person to fool is yourself. -- Richard Feynman
 

Offline SkyMaster

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Re: Oscilloscopes needed?
« Reply #16 on: September 24, 2015, 03:51:33 am »
To see wether or not I would need an oscilliscope to do this. I have software on my computer to pumpdata out of the COM port so I may be able to see the data output with an oscilliscope (if I had one) and was wondering if there was any way I could test this without one, or if there is a particular bandwidth oscilloscope that I may need.

In the early '90s, I was programming 68hc11 without having access to an oscilloscope in my home lab. I did a lot with only a DMM and a homemade Power Supply.

So no, you do not need an oscilloscope in order to figure out how to upload the code to a microcontroller.
 

Offline zerorisers

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Re: Oscilloscopes needed?
« Reply #17 on: September 24, 2015, 02:04:45 pm »

But does his computer even have a proper serial port connector? Nowadays pretty much everything is done over USB, isn't it?


It has the port directly on the motherboard, I am using no USB/serial converters. But no time when I googled the pin-out did I find a picture in a more 3D esk style. That will help a lot. Using the LED method I know there is a constant signal on pin 3 even when I am not sending anything.
That one picture does help quite a bit as just some dots in an arrangement doesn't tell me what direction it is facing, and I get confused easy.

(I can somehow troubleshoot the video on a FLIR board but I cant do this, Its the simple things that trouble me)


So if I where to get an oscilloscope ( I have used higher end ones from keysight through some seminars)  where would be the place to find one cheap with serial decoding?
 

Offline smbaker

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Re: Oscilloscopes needed?
« Reply #18 on: September 24, 2015, 03:42:14 pm »
Using the LED method I know there is a constant signal on pin 3 even when I am not sending anything.

Have you considered setting the baud rate to something really low, like 300 baud? That might give you a better shot at visually verifying which pin has the transmit data on it.

Another thing I'd check is to make sure that you're sending on the right serial port. Your motherboard could have unconnected serial port headers and you could be inadvertently talking to one of those instead of the port you think you are. Some programming libraries number parts starting at 0, some number them starting at 1. That's happened to me before, when I've wasted time debugging a circuit only to realize I'm not talking to the right port.

Also, you could consider building a logic probe (before I had a scope, I had a DIY logic probe built out of some commodity logic (probably a hex inverter) and a LED and a resistor) and poking around the logic side of the serial converter of the device you're interfacing to.

So if I where to get an oscilloscope ( I have used higher end ones from keysight through some seminars)  where would be the place to find one cheap with serial decoding?

Depends on what you mean by 'cheap'. I have a Rigol DS1054Z on order, which seems like a phenomenal value, like the DS1052E I had before that. I've used a scope to diagnose digital circuits before, to sanity-check that I had something connected right, and I've never needed serial decoding -- I just needed to see that there was pulses where I thought pulses should be.
 

Offline Howardlong

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Re: Oscilloscopes needed?
« Reply #19 on: September 24, 2015, 03:57:30 pm »

But does his computer even have a proper serial port connector? Nowadays pretty much everything is done over USB, isn't it?


It has the port directly on the motherboard, I am using no USB/serial converters. But no time when I googled the pin-out did I find a picture in a more 3D esk style. That will help a lot. Using the LED method I know there is a constant signal on pin 3 even when I am not sending anything.

You need to either switch the LED around and/or notice a difference in brightness when sending a continual stream, or be able to notice some tiny pulses, when sending odd characters from the keyboard. I'd drop your baudrate down to 9600 or so to at least you stand a chance when trying to "see" odd characters sent from your keyboard. It's not hard, just having some experience of doing it for five minutes will be enough.

Quote

So if I where to get an oscilloscope ( I have used higher end ones from keysight through some seminars)  where would be the place to find one cheap with serial decoding?

"Cheap": depends on how long your piece of string is, and how much you're willing to compromise. What is your definition of cheap?
 

Offline alsetalokin4017

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Re: Oscilloscopes needed?
« Reply #20 on: September 24, 2015, 08:54:14 pm »
If you give the manufacturer and part number of the motherboard, it might be possible to look it up and find the actual connector pinout from data on the internet.

To see an LED flashing visually it is going to have to flash at less than 30 Hz.
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Offline Howardlong

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Re: Oscilloscopes needed?
« Reply #21 on: September 24, 2015, 09:02:32 pm »

To see an LED flashing visually it is going to have to flash at less than 30 Hz.

Nope, 9600 is reasonably visible one character at a time, but that has to be from off to on, not on to off. Try it.

Edit: these were common currency 20 15 years ago (before reliable USB).

« Last Edit: September 24, 2015, 09:08:04 pm by Howardlong »
 


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