K2 - Strange Problem ?
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I think that I have found the problem, but have yet to work out a solution.
To combat the lack of TX audio system gain I have a 1 transistor pre-amp mounted on the microphone header plug on the front panel board. This gives about 9dB of gain which provides sufficient audio for the compressor IC and the VOX. The amplifier is supplied from the 5V pin on the header. This rail is the 5A supply which is used by the MCU logic, plus other functions. The amplifier only draws about 1mA, however because of noise on the 5A line, mainly from the LED bar graph I have had to heavily decouple the pre-amp supply to stop the noise from being superimposed on my speech. What I think is happening is that this decoupling is affecting the rise time of the 5A line which is used for the MCU reset amongst other things. I have tried reducing the value of decoupling. This seems to stop the "strange" problem, but I am back with the noise. It is a shame that there is no way to get at the +8V rail on the front panel board as that would be an ideal mic supply. The way things are looking I will have to put the pre-amp outside my K2 and power it separately. The only alternative seems to go back to shouting ! 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi Stewart
Try Rather than directly connecting the decoupling cap to the 5v supply, try feeding it via a 100 ohm (or so) resistor. at 1ma you will only drop .1 v but you have created a low pass filter for the noise. Rgds Andy Pevy G4XYW A future K2 owner (when the company bonus arrives). On Tuesday 30 November 2004 06:24, ext Stewart Baker wrote: > I think that I have found the problem, but have yet to work out a solution. > > To combat the lack of TX audio system gain I have a 1 transistor pre-amp > mounted on the microphone header plug on the front panel board. This gives > about 9dB of gain which provides sufficient audio for the compressor IC and > the VOX. The amplifier is supplied from the 5V pin on the header. This rail > is the 5A supply which is used by the MCU logic, plus other functions. > > The amplifier only draws about 1mA, however because of noise on the 5A > line, mainly from the LED bar graph I have had to heavily decouple the > pre-amp supply to stop the noise from being superimposed on my speech. > > What I think is happening is that this decoupling is affecting the rise > time of the 5A line which is used for the MCU reset amongst other things. > > I have tried reducing the value of decoupling. This seems to stop the > "strange" problem, but I am back with the noise. It is a shame that there > is no way to get at the +8V rail on the front panel board as that would be > an ideal mic supply. > > The way things are looking I will have to put the pre-amp outside my K2 and > power it separately. The only alternative seems to go back to shouting ! > > 73 > Stewart G3RXQ > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stewart Baker
On Tue, 30 Nov 2004 08:47:38 GMT, Stewart Baker wrote:
> On Tue, 30 Nov 2004 07:59:31 +0000, Andy Pevy wrote: >> Hi Stewart >> Try Rather than directly connecting the decoupling cap to the 5v supply, try >> feeding it via a 100 ohm (or so) resistor. at 1ma you will only drop .1 v >> but you have created a low pass filter for the noise. >> Rgds >> Andy Pevy >> G4XYW >> A future K2 owner (when the company bonus arrives). >> On Tuesday 30 November 2004 06:24, ext Stewart Baker wrote: >>> I think that I have found the problem, but have yet to work out a >>> solution. >>> To combat the lack of TX audio system gain I have a 1 transistor pre-amp >>> mounted on the microphone header plug on the front panel board. This gives >>> about 9dB of gain which provides sufficient audio for the compressor IC >>> and >>> the VOX. The amplifier is supplied from the 5V pin on the header. This >>> rail >>> is the 5A supply which is used by the MCU logic, plus other functions. >>> The amplifier only draws about 1mA, however because of noise on the 5A >>> line, mainly from the LED bar graph I have had to heavily decouple the >>> pre-amp supply to stop the noise from being superimposed on my speech. >>> What I think is happening is that this decoupling is affecting the rise >>> time of the 5A line which is used for the MCU reset amongst other things. >>> I have tried reducing the value of decoupling. This seems to stop the >>> "strange" problem, but I am back with the noise. It is a shame that there >>> is no way to get at the +8V rail on the front panel board as that would be >>> an ideal mic supply. >>> The way things are looking I will have to put the pre-amp outside my K2 >>> and >>> power it separately. The only alternative seems to go back to shouting ! >>> 73 >>> Stewart G3RXQ > Hi Andy, > Yes, that's what I have been trying. The noise is really a pulse as the LEDs > in > the display go on and off. Got up to 1.5k with a 47uF cap, however I now get > the > VOX switching on/off by it's self very occasionally, so I think that the 5A > line > does not appreciate any time constant being hung off it. > Latest thoughts are to use an op-amp instead of a transistor as I believe that > they have a greater immunity to supply noise than a simple common emitter > transistor amplifier. That should mean even less RC. > 73 > Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stewart Baker
At 01:24 AM 11/30/2004, Stewart Baker wrote...
>problem, but I am back with the noise. It is a shame that there is no way to get >at the +8V rail on the front panel board as that would be an ideal mic supply. The Auxbus connection between the RF board and front panel is unused. You could cut the trace on the RF board and use that to bring whatever you want across. I don't know if there are any future plans for a different front panel which might use that line. Alternately, there may be room to add an additional header pin at one end of the RF/FP connection to allow another signal. Worst case, you could airwire it with an inline connector. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Tue, 30 Nov 2004 07:18:23 -0500, Mike S wrote:
> At 01:24 AM 11/30/2004, Stewart Baker wrote... >> problem, but I am back with the noise. It is a shame that there is no way >> to get >> at the +8V rail on the front panel board as that would be an ideal mic >> supply. > The Auxbus connection between the RF board and front panel is unused. You > could cut the trace on the RF board and use that to bring whatever you want > across. I don't know if there are any future plans for a different front > panel which might use that line. Alternately, there may be room to add an > additional header pin at one end of the RF/FP connection to allow another > signal. Worst case, you could airwire it with an inline connector. Well spotted Mike ! I completely missed that route via Pin 7 on P1. I can feel my headache going already.... As you suggested I will cut the AUXBUS track on the RF board where it goes to the plug and wire the 8A rail to it. There appears to be plenty of decoupling already on that rail, but any more that I add should not upset things. It keeps everything clear of the MCU and other sensitive circuits. This new rail might be useful to supply other add-ons. I will then disconnect my pre-amp from the 5A supply, and use an airwire connection to Pin 7 on J1 to feed it. At this late stage in the K2 development I doubt if the AUXBUS signal to the Front panel will ever be used. I may have to tweak the pre-amp circuit values a bit for the increased supply voltage - but what the heck.. Again, many thanks for your valuable advice. I will keep you posted as to progress. 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stewart Baker
Stewart Baker wrote:
> The amplifier only draws about 1mA, however because of noise on the 5A line, > mainly from the LED bar graph I have had to heavily decouple the pre-amp supply > to stop the noise from being superimposed on my speech. > > What I think is happening is that this decoupling is affecting the rise time of > the 5A line which is used for the MCU reset amongst other things. Why don't you do this (must be viewed in fixed width font): 5V -------\\\\\\\----|----> to preamp large R | --- --- cap for decoupling | --- /// You will get better decoupling and isolate the capacitor from the 5V rail. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Tue, 30 Nov 2004 08:01:25 -0800, Vic Rosenthal wrote:
> Stewart Baker wrote: >> The amplifier only draws about 1mA, however because of noise on the 5A line, >> mainly from the LED bar graph I have had to heavily decouple the pre-amp >> supply >> to stop the noise from being superimposed on my speech. >> What I think is happening is that this decoupling is affecting the rise >> time of >> the 5A line which is used for the MCU reset amongst other things. > Why don't you do this (must be viewed in fixed width font): > 5V -------\\\\\\\----|----> to preamp > large R | > --- > --- cap for decoupling > | > --- > /// > You will get better decoupling and isolate the capacitor from the 5V rail. Thanks Vic, That's what I was doing, however, because anything capacitive slows the rise of the 5A rail, and hence the correct MCU initialisation, I was chasing my tail. A better solution has presented itself. 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stewart Baker
In a message dated 30/11/04 16:46:51 GMT Standard Time, [hidden email] writes: That's what I was doing, however, because anything capacitive slows the rise of the 5A rail, and hence the correct MCU initialisation, I was chasing my tail. This is a problem I have come across before about 5 years back where we had a newly developed repeater logic controlled by a PIC chip. I had the prototype running the local 2m repeater and the problem was that there were what appeared to be clock pulses appearing on the through audio of the logic. Attempts to decouple the 5V supply rail were disastrous in that it locked up the PIC chip. Eventually traced to the gremlin of delayed voltage rise on the chip due to charging of the decoupling capacitors. This is poison to the PIC chips as they require apparently a very fast rise time on the supply voltage. In our case the problem was self inflicted and was due to trying to be clever and using two regulators in tandem. Was cured by reverting to only one regulator fed direct from the incoming DC supply and only just enough decoupling to clean up the supply line. There is an additional support you can give the PIC chip in start up I discovered when trying to fault find on a partially defective chip. If instead of connecting the PIC chip MCLR pin direct to 5V (see U6 pin 1, the MCU on the K2 control board), connect it via a 10K ohm resistor and place a 4.7 to 10uF capacitor on the MCLR pin. This resultant delay allows all the voltages to stabilise before the chip is enabled. At least it is my belief of how the modification works. Additionally I added a diode with the anode to the MCLR pin across the 10K resistor to discharge the capacitor quickly in the event of a power interruption or the chip would again lock up. This was a change made to get over a particular problem with a PIC chip, but could be the answer to some odd glitches experienced recently. We now have this incorporated into our repeater logic as a standard. An entirely different usage, though one that could have parallels. Perhaps Eric or Wayne at Elecraft could comment. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Tue, 30 Nov 2004 15:45:37 EST, [hidden email] wrote:
> In a message dated 30/11/04 16:46:51 GMT Standard Time, > [hidden email] writes: > That's what I was doing, however, because anything capacitive slows the rise > of > the 5A rail, and hence the correct MCU initialisation, I was chasing my tail. > > > This is a problem I have come across before about 5 years back where we had a > newly developed repeater logic controlled by a PIC chip. > I had the prototype running the local 2m repeater and the problem was that > there were what appeared to be clock pulses appearing on the through audio of > the logic. Attempts to decouple the 5V supply rail were disastrous in that it > locked up the PIC chip. Eventually traced to the gremlin of delayed voltage > rise on the chip due to charging of the decoupling capacitors. This is poison > to the PIC chips as they require apparently a very fast rise time on the > supply voltage. In our case the problem was self inflicted and was due to > trying to be clever and using two regulators in tandem. Was cured by > reverting to only one regulator fed direct from the incoming DC supply and > only just enough decoupling to clean up the supply line. > There is an additional support you can give the PIC chip in start up I > discovered when trying to fault find on a partially defective chip. > If instead of connecting the PIC chip MCLR pin direct to 5V (see U6 pin 1, > the MCU on the K2 control board), connect it via a 10K ohm resistor and place > a 4.7 to 10uF capacitor on the MCLR pin. This resultant delay allows all the > voltages to stabilise before the chip is enabled. At least it is my belief of > how the modification works. Additionally I added a diode with the anode to > the MCLR pin across the 10K resistor to discharge the capacitor quickly in > the event of a power interruption or the chip would again lock up. This was a > change made to get over a particular problem with a PIC chip, but could be > the answer to some odd glitches experienced recently. We now have this > incorporated into our repeater logic as a standard. An entirely different > usage, though one that could have parallels. > Perhaps Eric or Wayne at Elecraft could comment. > Bob, G3VVT Hi Bob, Thank you for the detailed explanation of your experiences with PIC resets. Microchip data sheets/books show a number of ways that a reset can be achieved on their PIC's. Tying MCLR and VDD together is unsatisfactory. The way you describe with the R,C and diode gives a very reliable reset everytime and is independent of the supply rise time. The diode makes sure that the MCLR line always starts from a known state by discharging the C. As you mention glitches on the supply also need to be addressed. Although not directly involved with the "strange problem" I consider the MCU reset a point of weakness in the K2 design, and am contemplating modifying the Control board to add a proper reset. I too would be interested in comment from Eric or Wayne. 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I've had trouble with PIC chips that don't have the "brownout reset"
function. The RC circuit on the reset line (mentioned by G3VVT below) is a good idea. The CPU can also go into never-never land if the Vcc droops a little due to a brief line voltage drop-out. Now a days, I use an external brownout reset chip for micros that don't have it built in. These are very small three terminal devices. They are good insurance against getting into an invalid state due to power glitches. The watchdog timer can also be helpful to reset from a lock-up condition without extra hardware. This assumes the micro does power up correctly so it can initiallize the watchdog timer. Later if something goes wrong, it can issue a software reset. This is also good for recovering from very rare and almost-impossible to catch software "issues". 73/ Bob - W5BIG ----- Original Message ----- From: "Stewart Baker" <[hidden email]> To: <[hidden email]>; <[hidden email]> Cc: <[hidden email]> Sent: Wednesday, December 01, 2004 1:00 AM Subject: Re: [Elecraft] K2 - Strange Problem ? On Tue, 30 Nov 2004 15:45:37 EST, [hidden email] wrote: > In a message dated 30/11/04 16:46:51 GMT Standard Time, > [hidden email] writes: > That's what I was doing, however, because anything capacitive slows the rise > of > the 5A rail, and hence the correct MCU initialisation, I was chasing my tail. > > > This is a problem I have come across before about 5 years back where we had a > newly developed repeater logic controlled by a PIC chip. > I had the prototype running the local 2m repeater and the problem was that > there were what appeared to be clock pulses appearing on the through audio of > the logic. Attempts to decouple the 5V supply rail were disastrous in that it > locked up the PIC chip. Eventually traced to the gremlin of delayed voltage > rise on the chip due to charging of the decoupling capacitors. This is poison > to the PIC chips as they require apparently a very fast rise time on the > supply voltage. In our case the problem was self inflicted and was due to > trying to be clever and using two regulators in tandem. Was cured by > reverting to only one regulator fed direct from the incoming DC supply and > only just enough decoupling to clean up the supply line. > There is an additional support you can give the PIC chip in start up I > discovered when trying to fault find on a partially defective chip. > If instead of connecting the PIC chip MCLR pin direct to 5V (see U6 pin 1, > the MCU on the K2 control board), connect it via a 10K ohm resistor and place > a 4.7 to 10uF capacitor on the MCLR pin. This resultant delay allows all the > voltages to stabilise before the chip is enabled. At least it is my belief of > how the modification works. Additionally I added a diode with the anode to > the MCLR pin across the 10K resistor to discharge the capacitor quickly in > the event of a power interruption or the chip would again lock up. This was a > change made to get over a particular problem with a PIC chip, but could be > the answer to some odd glitches experienced recently. We now have this > incorporated into our repeater logic as a standard. An entirely different > usage, though one that could have parallels. > Perhaps Eric or Wayne at Elecraft could comment. > Bob, G3VVT Hi Bob, Thank you for the detailed explanation of your experiences with PIC resets. Microchip data sheets/books show a number of ways that a reset can be achieved on their PIC's. Tying MCLR and VDD together is unsatisfactory. The way you describe with the R,C and diode gives a very reliable reset everytime and is independent of the supply rise time. The diode makes sure that the MCLR line always starts from a known state by discharging the C. As you mention glitches on the supply also need to be addressed. Although not directly involved with the "strange problem" I consider the MCU reset a point of weakness in the K2 design, and am contemplating modifying the Control board to add a proper reset. I too would be interested in comment from Eric or Wayne. 73 Stewart G3RXQ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stewart Baker
On Nov 30, 2004, at 1:24 AM, Stewart Baker wrote: > t is a shame that there is no way to get > at the +8V rail on the front panel board as that would be an ideal mic > supply. I brought the +8V rail from the RF board up to a two-pin jumper. I then plug this in to once side of the Mic jumper block. This supplies the +8v I need to power my single-message voice keyer that I use for contests. (this works interchangably with my Kenwood TS-430S) It is possible to separate the front panel and the RF board, but since I rarely do so, it isn't much of a problem. Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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