[time-nuts] Re: HP Z3801A project update
Tom Holmes wrote: "I am curious about one part of the warmup process. At around 7 minutes, the power jumps up radically, which you attribute to the outer oven kicking in. It has often been stated on this list that the outer oven was intended for use during really cold starts, which I would expect should cause it to kick on almost immediately during a very cold start. I am assuming your start was from room temperature. For a room temp start, I wouldn't expect it to kick on at all if it's purpose was as reported. Or do I have the oven functions reversed?" By "cold start," I mean powering it up when the system has been off for some time, and everything is near ambient, regardless of temperature. Right now, the system is indoors, at comfortable room temperature. Normally, it resides in the garage, pretty much at outdoor conditions. I have observed and studied the behavior quite often over the years, and especially, I learned a lot about the innards long ago, when the opamp that controls the inner oven had crapped out. I had to take the whole thing apart, deep into the guts, while not damaging anything. The surgery went well, but I sure would not want to do it again. I've never worried about the startup, since the AC supply had no problem at all firing it up. Now that I'm finally wrapping up details like external DC running and starting, I've had to scrutinize the situation. Here's my take on what it does, and why. To reduce startup power (besides inrush current to charge caps and get the DC-DC converters going), the ovens are sequenced. The priority goes to the inner one first, to get the system operational ASAP. If say, it was not a double oven system, but only a single, the OCXO would just do its thing and be ready to go in short order, regardless of ambient temperature. The outer oven is the icing on the cake, so to speak - it catches up later, to provide the higher ultimate stability. It's also necessarily slower (unless a lot more power and a bigger heater element was used), because of the much larger thermal mass and area involved. The outer oven is always active in steady state conditions. I can see how there may be some confusion and misinterpretation about its role and operation, depending on when observations are made, and the initial conditions. If one were to be fooling around with power ups and downs, trying to figure out what it's doing, the actual temperatures inside can be all over the place, and change the apparent response. For instance, I found that the system had to be shut down for several hours to be sure of near-ambient conditions for my cold start tests. Restarting a test run too soon, say, while the inner oven is still near setpoint, may make it appear that the outer oven comes on immediately at power up. In reality, it just means the first step has been skipped or greatly shortened. Regardless of the initial conditions, the operating sequence is the same. All the circuitry and the inner oven are immediately powered up. When the inner oven reaches its setpoint, it signals the brain that it's ready, then after a short time delay (maybe up to 15 sec or so - hard to tell), the outer oven driver is enabled. The actual conditions at power up simply modify the heater load currents and timing. After a power dropout (assuming already in steady state) of a few seconds, the whole power up sequence may be all done by the time you can make a measurement, and barely noticeable. One thing I've been curious about is what's going on at the very moment the outer oven turns on (during cold start). The power jumps dramatically to some peak level, then quickly (a matter of seconds) drops to a slightly lower level, then very slowly as it continues. I haven't been able to catch the actual peak value, with just DVM observation, but I know it's pretty big, and quick. This is most likely an artifact of electronic response, not thermal. I believe it's caused by an overshoot in the oven's PID loop during activation. I'll have more to say next time on the thermal stuff and the power system in the Z3801A. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP Z3801A project update
Hi One would guess that they delay going “full power” so as not to hammer the main power supply quite so hard at start up. Bob > On Jan 29, 2022, at 2:27 PM, Tom Holmes wrote: > > HI Ed & Ed... > > Thanks for the plot. The dive towards zero just before the spike s > surprising; maybe a funky data point? > > Anyway, I'm not doubting that the observations are correct, just curious > about the timing and source of that power spike. Like maybe the controller > decided it wasn't heating fast enough? > > Tom Holmes, N8ZM > > -Original Message- > From: Ed Palmer > Sent: Saturday, January 29, 2022 11:07 AM > To: time-nuts@lists.febo.com > Subject: [time-nuts] Re: HP Z3801A project update > > On 2022-01-29 2:30 AM, "Tom Holmes" wrote: >> Ed... >> >> Very good data! >> >> I am curious about one part of the warmup process. At around 7 minutes, the >> power jumps up radically, which you attribute to >> the outer oven kicking in. It has often been stated on this list that the >> outer oven was intended for use during really cold >> starts, which I would expect should cause it to kick on almost immediately >> during a very cold start. I am assuming your start >> was from room temperature. For a room temp start, I wouldn't expect it to >> kick on at all if it's purpose was as reported. Or >> do I have the oven functions reversed? >> >> Tom Holmes, N8ZM > > I can confirm Ed's tests. Attached is a similar test that I did on my > Z3801A. If it matters, mine is the 24V nominal version. My test was > done at 27V. The power supply was an HP6622A with GPIB. I wrote a > program to query the current being drawn each second. The current value > was later converted to power. > > Ed > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: electronics question or how not to fry my raspberry pi
I endorse Dave's suggestion (below) . The resistive divider is simple but slows down the edge rate which may be undesirable especially if the input isnt a schmitt. The MOSFET solution is the most appropriate. take a look what is inside packaged translators... just that. On 29/01/2022 10:33 pm, Dave B via time-nuts wrote: You can actually use a single small N channel MOSFET (2N7000 or similar) with it's Gate connected to the lower Vcc via, say, a 1k resistor. (Not strictly needed, but with long leads, it helps prevent HF transient oscillation. Then use it's Source as the lower voltage data line, and it's Drain as the higher voltage data line. You get two way communication like that too. (Hint: Consider the parasitic diode between the Drain and Source.) Action: everything floats high to 3.3V or 5V. FET is not conducting. Pull the 3.3V side down, FET turns on (Gate is +3.3V wrt Source) and the Drain pulls down the 5V side, note the 5V side pull down current will pass to the 3.3V side, so take care that the 3.3V pull down port is capable of sinking that current as well... Pull the 5.5V side down, Parasitic diode conducts, pulling down the 3.3V side that in turn also turns on the FET, providing a lower impedance path "backwards" though the device. As above, the 5V side "sinks" the 3.3V pull down current. It all works magically well. Many of the simple multichannel bus voltage translators that do NOT provide galvanic isolation, are just like that internally, but with pull up's to the two Vcc rails, and some extra protection diodes etc. I've done that between 3.3V and 5V systems, and between 5V and 9V logic systems with discrete parts, It works very well indeed. To a limited degree, the same "trick" also works with many bipolar transistors, with a diode from Emitter to Collector, and a better choice of resistor on the Base. Have Fun. Dave G8KBV ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: electronics question or how not to fry my raspberry pi
Those diodes are so robust that a PIC connected the wrong way to a 5V 1 Amp PSU was protected by all these diodes conducting in parallel and current limiting the PSU. The PIC appeared to have survived (although I chucked it anyway, just in case) Andy www.g4jnt.com On Sat, 29 Jan 2022 at 18:56, Robert Atkinson via time-nuts < time-nuts@lists.febo.com> wrote: > You can run the PicDiv on 3.3 V and connect the 5V signal to the PicDiv > input via a series resistor between 1k and 10k. Put the resistor at the > PicDiv end of the connection. > The PIC has protection diodes on it's input These clamp the input to the > supply. The series resisor limits the current. This is robust. There are > thousands of devices out there with a pin conneted to the mains with just a > series resistor. t's used for zerocrossing detection or monitoring the > mains frequency. > Robert G8RPI. > > On Friday, 28 January 2022, 20:06:20 GMT, folkert < > folk...@vanheusden.com> wrote: > > Hi, > > I bought a GPSDO. It outputs somewhere around 3V. This is connected to a > picdiv and then to a raspberry pi. The picdiv is happy with 3.3v, the rpi > as well. All good. > > Now I bought a "Square Wave Amplifier" by BG7TBL ( > https://www.aliexpress.com/item/4000192799858.html?gatewayAdapt=glo2nld=a2g0o.9042311.0.0.3d764c4dMZPAX8 > ). Documentation I could find was a bit vague about the > output voltage but I measured 5v with a scope (see > https://vanheusden.com/permshare/scope.png - the scope software says > 2MHz but output is really 10MHz). > > I did not study electronics, am only a electronics-hobbyist so bare with > me when this is a dumb question. > > The RPI doesn't like 5v on its GPIO pins. > So I wonder: > - can I feed the picdiv 5v on its GPIO pin while giving it a 3.3v > voltage so that it outputs 3.3v as well to the rpi pins? > - or should I use a voltage divider? I was thinking of a 4.7k ohm and > 8.2k ohm resistor giving slightly less than 3.2v - will that work? or > will that attenuate the signal too much? The 50 ohm bnc cable between > the amplifier and the rpi is 3m long. Anything else I should be aware > of? > > > Regards, > > Folkert van Heusden > PD9FVH > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP Z3801A project update
HI Ed & Ed... Thanks for the plot. The dive towards zero just before the spike s surprising; maybe a funky data point? Anyway, I'm not doubting that the observations are correct, just curious about the timing and source of that power spike. Like maybe the controller decided it wasn't heating fast enough? Tom Holmes, N8ZM -Original Message- From: Ed Palmer Sent: Saturday, January 29, 2022 11:07 AM To: time-nuts@lists.febo.com Subject: [time-nuts] Re: HP Z3801A project update On 2022-01-29 2:30 AM, "Tom Holmes" wrote: > Ed... > > Very good data! > > I am curious about one part of the warmup process. At around 7 minutes, the > power jumps up radically, which you attribute to > the outer oven kicking in. It has often been stated on this list that the > outer oven was intended for use during really cold > starts, which I would expect should cause it to kick on almost immediately > during a very cold start. I am assuming your start > was from room temperature. For a room temp start, I wouldn't expect it to > kick on at all if it's purpose was as reported. Or > do I have the oven functions reversed? > > Tom Holmes, N8ZM I can confirm Ed's tests. Attached is a similar test that I did on my Z3801A. If it matters, mine is the 24V nominal version. My test was done at 27V. The power supply was an HP6622A with GPIB. I wrote a program to query the current being drawn each second. The current value was later converted to power. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: HP Z3801A project update
On 2022-01-29 2:30 AM, "Tom Holmes" wrote: Ed... Very good data! I am curious about one part of the warmup process. At around 7 minutes, the power jumps up radically, which you attribute to the outer oven kicking in. It has often been stated on this list that the outer oven was intended for use during really cold starts, which I would expect should cause it to kick on almost immediately during a very cold start. I am assuming your start was from room temperature. For a room temp start, I wouldn't expect it to kick on at all if it's purpose was as reported. Or do I have the oven functions reversed? Tom Holmes, N8ZM I can confirm Ed's tests. Attached is a similar test that I did on my Z3801A. If it matters, mine is the 24V nominal version. My test was done at 27V. The power supply was an HP6622A with GPIB. I wrote a program to query the current being drawn each second. The current value was later converted to power. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: electronics question or how not to fry my raspberry pi
You can run the PicDiv on 3.3 V and connect the 5V signal to the PicDiv input via a series resistor between 1k and 10k. Put the resistor at the PicDiv end of the connection. The PIC has protection diodes on it's input These clamp the input to the supply. The series resisor limits the current. This is robust. There are thousands of devices out there with a pin conneted to the mains with just a series resistor. t's used for zerocrossing detection or monitoring the mains frequency. Robert G8RPI. On Friday, 28 January 2022, 20:06:20 GMT, folkert wrote: Hi, I bought a GPSDO. It outputs somewhere around 3V. This is connected to a picdiv and then to a raspberry pi. The picdiv is happy with 3.3v, the rpi as well. All good. Now I bought a "Square Wave Amplifier" by BG7TBL ( https://www.aliexpress.com/item/4000192799858.html?gatewayAdapt=glo2nld=a2g0o.9042311.0.0.3d764c4dMZPAX8 ). Documentation I could find was a bit vague about the output voltage but I measured 5v with a scope (see https://vanheusden.com/permshare/scope.png - the scope software says 2MHz but output is really 10MHz). I did not study electronics, am only a electronics-hobbyist so bare with me when this is a dumb question. The RPI doesn't like 5v on its GPIO pins. So I wonder: - can I feed the picdiv 5v on its GPIO pin while giving it a 3.3v voltage so that it outputs 3.3v as well to the rpi pins? - or should I use a voltage divider? I was thinking of a 4.7k ohm and 8.2k ohm resistor giving slightly less than 3.2v - will that work? or will that attenuate the signal too much? The 50 ohm bnc cable between the amplifier and the rpi is 3m long. Anything else I should be aware of? Regards, Folkert van Heusden PD9FVH ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: electronics question or how not to fry my raspberry pi
You can actually use a single small N channel MOSFET (2N7000 or similar) with it's Gate connected to the lower Vcc via, say, a 1k resistor. (Not strictly needed, but with long leads, it helps prevent HF transient oscillation. Then use it's Source as the lower voltage data line, and it's Drain as the higher voltage data line. You get two way communication like that too. (Hint: Consider the parasitic diode between the Drain and Source.) Action: everything floats high to 3.3V or 5V. FET is not conducting. Pull the 3.3V side down, FET turns on (Gate is +3.3V wrt Source) and the Drain pulls down the 5V side, note the 5V side pull down current will pass to the 3.3V side, so take care that the 3.3V pull down port is capable of sinking that current as well... Pull the 5.5V side down, Parasitic diode conducts, pulling down the 3.3V side that in turn also turns on the FET, providing a lower impedance path "backwards" though the device. As above, the 5V side "sinks" the 3.3V pull down current. It all works magically well. Many of the simple multichannel bus voltage translators that do NOT provide galvanic isolation, are just like that internally, but with pull up's to the two Vcc rails, and some extra protection diodes etc. I've done that between 3.3V and 5V systems, and between 5V and 9V logic systems with discrete parts, It works very well indeed. To a limited degree, the same "trick" also works with many bipolar transistors, with a diode from Emitter to Collector, and a better choice of resistor on the Base. Have Fun. Dave G8KBV On 29/01/2022 08:30, time-nuts-requ...@lists.febo.com wrote: I find that the best way to handle these translations is to use one of TI's level translators ... each chip has two power supply rails, and translation is done transparently across the chip, and there is good max voltage overprotection on both sides as well. I use them a lot to handle 5V <-> 3.3V level issues. Try the SN74LVC8T245PWR for unidirectional level translating . They also have some bidirectional ones ... --Andrew -- Created on and sent from a Unix like PC running and using free and open source software: ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: electronics question or how not to fry my raspberry pi
On 28/01/2022 19:41, folkert wrote: Hi, [] The RPI doesn't like 5v on its GPIO pins. So I wonder: - can I feed the picdiv 5v on its GPIO pin while giving it a 3.3v voltage so that it outputs 3.3v as well to the rpi pins? - or should I use a voltage divider? I was thinking of a 4.7k ohm and 8.2k ohm resistor giving slightly less than 3.2v - will that work? or will that attenuate the signal too much? The 50 ohm bnc cable between the amplifier and the rpi is 3m long. Anything else I should be aware of? Regards, Folkert van Heusden PD9FVH Folkert, In similar circumstances I've used a resistive divider and it's worked exactly as expected. For such short cables there are unlikely to be any other effects you need to take care of. You might like to see what the voltage levels are if you terminate the 50-ohm cable with a 47-ohm resistor - it /may/ drop to 2.5V peak-to-peak. I would simply try it and see. Of course, if the idea is to send PPS to the RPi getting the appropriate GPS devices would be my preferred solution! Oh, just looked, I would expect to see a square-wave, not the near sine-wave your 'scope trace shows. Is it nearer to square with a much faster timebase? Cheers, David -- SatSignal Software - Quality software for you Web: https://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
