Re: [time-nuts] Frequency divider design critique request
[Context is filtering on inputs from switches.] Could somebody tell me why we are doing anything fancy at all? What's wrong with just a simple pullup? I can think of two cases that might be interesting. One is signal integrity. There might be enough crosstalk to cause troubles. This is a 4 layer board. Right? Unless the traces from the switch to the mux chip wrap around some high speed signal there isn't likely to be a problem. I'm not a signal integrity wizard, but the ballpark is that you only need a few trace widths of separation between agressor/source and victim/receiver. This case is slightly ugly since the pullup is not low impedance like a typical driver. So the question becomes how small a pullup do we need to maintain good signal integrity? Or how far from a nearby trace do we have to be with a given pullup? If the coupling is primarily capacitive, then we have a C-R high pass filter. I'm not sure that's valid, but it is easy to analyze. I should be smart enough to work this out, but it's late. HC is pretty slow. AC might be fast enough to make things interesting. But this only matters if the switch traces run parallel to a trace that is active for a significant length. What is the (ballpark) output impedance of a CMOS driver? What's the input capacitance on a CMOS gate? (It's in parallel with the R, making a C-C divider at high frequencies.) The other possible complication is trying to keep a clean output signal when the switch changes state. I'm assuming we don't really care what happens while the contacts are bouncing between switch settings. If we do, then we need serious switch debouncing and synchronization. I don't think anybody has mentioned this tangle. All the switch inputs I've worked with recently have been a simple pullup/down. They usually go into a small CPU using the internal pullups and software debouncing. I have heard war stories of cross talk on reset signals. They often wander all over the board and since they are slow, they often get overlooked when checking for crosstalk. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency divider design critique request
Hal Murray wrote: [Context is filtering on inputs from switches.] Could somebody tell me why we are doing anything fancy at all? What's wrong with just a simple pullup? Pull down required because of thumbwheel switch encoding. I can think of two cases that might be interesting. One is signal integrity. There might be enough crosstalk to cause troubles. This is a 4 layer board. Right? Unless the traces from the switch to the mux chip wrap around some high speed signal there isn't likely to be a problem. The 10MHz clock tracks have been routed well clear of everything else. I'm not a signal integrity wizard, but the ballpark is that you only need a few trace widths of separation between agressor/source and victim/receiver. This case is slightly ugly since the pullup is not low impedance like a typical driver. So the question becomes how small a pullup do we need to maintain good signal integrity? Or how far from a nearby trace do we have to be with a given pullup? If the coupling is primarily capacitive, then we have a C-R high pass filter. I'm not sure that's valid, but it is easy to analyze. I should be smart enough to work this out, but it's late. HC is pretty slow. AC might be fast enough to make things interesting. But this only matters if the switch traces run parallel to a trace that is active for a significant length. What is the (ballpark) output impedance of a CMOS driver? What's the input capacitance on a CMOS gate? (It's in parallel with the R, making a C-C divider at high frequencies.) 10-20 ohms. 5-10pF. The other possible complication is trying to keep a clean output signal when the switch changes state. I'm assuming we don't really care what happens while the contacts are bouncing between switch settings. If we do, then we need serious switch debouncing and synchronization. I don't think anybody has mentioned this tangle. RC filter followed by a Schmitt trigger IC (74HC14) can debounce the switch contacts effectively if RC product is large enough. A shift register (clocked at 1MHz in this case)is required to synchronise each mux control input if synchronisation is required. Using a shift register is slightly simpler than using a dual FF as only need to connect clock plus input and output. All the switch inputs I've worked with recently have been a simple pullup/down. They usually go into a small CPU using the internal pullups and software debouncing. No cpu available. I have heard war stories of cross talk on reset signals. They often wander all over the board and since they are slow, they often get overlooked when checking for crosstalk. Using an emitter follower to buffer the reset circuit RC node has led to VHF oscillation problems with capacitive load on emitter (track C) with collector and base at RF ground. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency divider design critique request
Magnus is on vacation and has some (net) connectivity problems. I would expect him to be back online within a day or two. -- Björn On Wed, 2008-07-16 at 18:27 +0100, David C. Partridge wrote: I'm waiting to see what Magnus Danielson has to say, as it was he after all who suggested adding caps in parallel to the pull-downs, and also series resistors. Thinking about it retrospect, I think he may have meant the series resistors to go between the pull-downs and the chip, rather than where the schematic fragment showed them. I don't *think* switch bounce is an issue here, as it will all settle to the right answer pretty sharply. Magnus, are you there? Cheers Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Frequency divider design critique request
David C. Partridge wrote: I'm waiting to see what Magnus Danielson has to say, as it was he after all who suggested adding caps in parallel to the pull-downs, and also series resistors. Thinking about it retrospect, I think he may have meant the series resistors to go between the pull-downs and the chip, rather than where the schematic fragment showed them. I don't *think* switch bounce is an issue here, as it will all settle to the right answer pretty sharply. Magnus, are you there? Cheers Dave Dave Switch bounce could be an issue if one wished to switch cleanly to another frequency output without incurring extraneous transitions during the changeover from one frequency to another. A hex D(74HC174) or an octal D(74HC374 74HC574) could be used to synchronise debounced multiplexer select inputs. Another issue is that all BCD switch contacts will not make or break at the same time. Also the debounce filters will not all settle simultaneously. Thus a debounced enable pushbutton may also be required. When the enable pushbutton is depressed the current state of the selector switches is latched. In this case only the enable pushbutton need be debounced. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
The Noritake display looks great. I am hoping that a kit of this proposed Thunderbolt monitor with the Noritake display will be made available through TARP in the near future. I am sure that many of the Thunderbolts which recently became available would benefit from such a kit. Jeff - Original Message - From: Didier Juges [EMAIL PROTECTED] To: Time-Nuts time-nuts@febo.com Sent: Tuesday, July 15, 2008 12:47 AM Subject: [time-nuts] Thunderbolt monitor I made a second version (same firmware) of the Thunderbolt monitor. This one uses the plastic DIP version of the processor mounted on a small Radio Shack proto board and it uses a gorgeous Noritake Vacuum Fluorescent display. The interface between the Noritake and any ordinary LCD display is the same ( as far as pin-out is concerned), except that the Noritake does not have a contrast adjustment. Otherwise, the firmware is the same, once the differences are accounted for. The Noritake is generally much faster than most 2 line LCDs when updating the data, but requires a little more time to initialize themselves at power up. My software can drive either display without modification. The Noritake displays have a software command to adjust the brightness down to half, and that's it. My firmware does not take advantage of that feature, which I find relatively useless, but may prolong the life of the display. The VFDs only have a few years of life under continuous operation, so dimming the display or turning it off altogether when not needed might be a good idea. See pictures at http://www.ko4bb.com/Timing/GPSMonitor/ Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
One issue with the Noritake display (common to all VFD devices) is that it draws over 100mA of current at 5V. A 3 terminal linear regulator running from 12V will need a reasonable heat sink to operate. A better choice would be a small switching regulator such as the LT1375 which I have used in a great many products. It's a small 8 pin device that requires only a handful of external components to convert 12V to 5 with excellent efficiency (no heat sink required). I may lay out the PWB for both types of regulators, depending on the type of display you want to use. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of jshank Sent: Wednesday, July 16, 2008 8:59 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt monitor The Noritake display looks great. I am hoping that a kit of this proposed Thunderbolt monitor with the Noritake display will be made available through TARP in the near future. I am sure that many of the Thunderbolts which recently became available would benefit from such a kit. Jeff - Original Message - From: Didier Juges [EMAIL PROTECTED] To: Time-Nuts time-nuts@febo.com Sent: Tuesday, July 15, 2008 12:47 AM Subject: [time-nuts] Thunderbolt monitor I made a second version (same firmware) of the Thunderbolt monitor. This one uses the plastic DIP version of the processor mounted on a small Radio Shack proto board and it uses a gorgeous Noritake Vacuum Fluorescent display. The interface between the Noritake and any ordinary LCD display is the same ( as far as pin-out is concerned), except that the Noritake does not have a contrast adjustment. Otherwise, the firmware is the same, once the differences are accounted for. The Noritake is generally much faster than most 2 line LCDs when updating the data, but requires a little more time to initialize themselves at power up. My software can drive either display without modification. The Noritake displays have a software command to adjust the brightness down to half, and that's it. My firmware does not take advantage of that feature, which I find relatively useless, but may prolong the life of the display. The VFDs only have a few years of life under continuous operation, so dimming the display or turning it off altogether when not needed might be a good idea. See pictures at http://www.ko4bb.com/Timing/GPSMonitor/ Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
Regarding the VFD display, although they may be very different one manufacturer to another, I can definitely dispute a prior statement made that VFDs in general have a short lifetime and become dim. They are universally used in VCRs, DVD players, microwave ovens, and some clocks. I have never had one become dim or burn out. The displays in my appliances are on even when the rest of the appliance is off. I have never seen one become dim even after 15 years of on-time. I look forward to your project. 73, Jeffrey Pawlan, WA6KBL ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
Yeah, those Noritake parts are very nice. I wouldn't expect trouble from one. There is a slight possibility of additional EMI versus an LCD, obviously nothing that would cause trouble at the end of an RS232 cable. -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Jeffrey Pawlan Sent: Wednesday, July 16, 2008 8:40 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt monitor Regarding the VFD display, although they may be very different one manufacturer to another, I can definitely dispute a prior statement made that VFDs in general have a short lifetime and become dim. They are universally used in VCRs, DVD players, microwave ovens, and some clocks. I have never had one become dim or burn out. The displays in my appliances are on even when the rest of the appliance is off. I have never seen one become dim even after 15 years of on-time. I look forward to your project. 73, Jeffrey Pawlan, WA6KBL ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
On Jul 16, 2008, at 10:46 PM, Didier Juges wrote: One issue with the Noritake display (common to all VFD devices) is that it draws over 100mA of current at 5V. A 3 terminal linear regulator running from 12V will need a reasonable heat sink to operate. A better choice would be a small switching regulator such as the LT1375 which I have used in a great many products. It's a small 8 pin device that requires only a handful of external components to convert 12V to 5 with excellent efficiency (no heat sink required). I may lay out the PWB for both types of regulators, depending on the type of display you want to use. Didier KO4BB Why would you run this external box off of 12 volts? Do you have portable use in mind? I ask because to my way of thinking, I would provide the display/ processor box with 5 volts straight out of a wall wart; I've probably got a dozen in that voltage range lying around (left over from ZIP drives). The only use for 12 volts in the display box would be for the RS232, and that can come from a MAX232 chip. Seems like a simpler approach to me. If I really wanted portable, the 12-5v unit would be external. Tom Frank KA2CDK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt monitor
My preference is usually to have a voltage regulator on the board where the expensive electronics is, simply because I use adjustable bench supplies for testing and I also own and use a large number of 9 to 12V wall warts such that I have blown great many parts by inadvertently putting 9 or 12V into a 5V gizmo. Also, most of my processor boards take advantage of the built-in A/D converter, and a local stable 5V source is a good design practice that avoids a number of problems down the road. So it's been my practice to put a 5V regulator, needed or not :-) Now, the Silabs chips run off 3V nominal and have their own, relatively stable 2.5V reference, so that problem also mostly goes away. In this case, since the group buy Thunderbolt comes with a multi-output supply which includes 5V, we could use that directly I guess. It just had not occurred to me to do that... My original red box Thunderbolt runs off 28V, so that one will definitely need its own switching regulator. Regarding the RS-232, the monitor only needs to convert the RS-232 to 0-3V logic, so 12V is not needed there either. In any event, a separate supply would be a waste and is not necessary. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Thomas A. Frank Sent: Wednesday, July 16, 2008 11:06 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt monitor On Jul 16, 2008, at 10:46 PM, Didier Juges wrote: One issue with the Noritake display (common to all VFD devices) is that it draws over 100mA of current at 5V. A 3 terminal linear regulator running from 12V will need a reasonable heat sink to operate. A better choice would be a small switching regulator such as the LT1375 which I have used in a great many products. It's a small 8 pin device that requires only a handful of external components to convert 12V to 5 with excellent efficiency (no heat sink required). I may lay out the PWB for both types of regulators, depending on the type of display you want to use. Didier KO4BB Why would you run this external box off of 12 volts? Do you have portable use in mind? I ask because to my way of thinking, I would provide the display/ processor box with 5 volts straight out of a wall wart; I've probably got a dozen in that voltage range lying around (left over from ZIP drives). The only use for 12 volts in the display box would be for the RS232, and that can come from a MAX232 chip. Seems like a simpler approach to me. If I really wanted portable, the 12-5v unit would be external. Tom Frank KA2CDK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
