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 Post subject: Scope clock
PostPosted: May Sun 27, 2018 2:23 pm 
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Well since I got the CRT driver circuit perfected and the previous clock finished I think it is time to build a version for work using a 3RP1 CRT and a OS8-CU scope which for me isn't really usable as a scope.

I'll remove all the electronics and keep only what is needed for the clock and CRT driver.

What I may do is purchase the clock board, build it then take the scope to work and see if a 3" CRT is big enough.

Now before I do this. Is there any reason why I should not use this scope for the project?

More to follow.



EDIT:

Here's a couple of pictures.

As can be seen the scope in stock form has enough bandwidth to properly display the clock if I use the AC coupling, but doesn't display quite right when using DC coupling as it is more triangular in shape with the right side and bottom expanded more than the left side and top.

Suppose I have a circuit issue causing that. Perhaps a mismatched tube?

But that doesn't really matter as I am going to install the CRT driver in it anyways.

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EDIT 2:

Thought I had run into a problem when I looked on the transformer at the diagram and the center tap of the 6.3Vac winding is grounded to a common ground terminal shared by the HV winding, but then I thought about it and I can get this isolated +/- 5V DC-DC converter.

https://www.mouser.com/ProductDetail/TR ... fLCQ%3d%3d

Datasheet

https://www.mouser.com/datasheet/2/687/ ... 317808.pdf

Use the full 6.3Vac winding with bridge rectifier and a filter cap then feed the converter to provide the proper +/- 5Vdc the circuit needs to function properly.

Schematic

Attachment:
Supply.png
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 Post subject: Re: Scope clock
PostPosted: Jun Fri 01, 2018 7:25 pm 
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Parts are on order. Gonna build the CRT driver stock except the +/- 5v supply the B+ filter cap which I upped to 100uF and the caps for the voltage doubler which I upped to 22uF.

Once built I will test it and see how well it works then tweak it as needed for best operation.

This of course only needs to work with the 3RP1A so I won't be experimenting with it like I did with the last CRT driver.

I'll be mounting the CRT driver close to the power transformer which is at the rear of the CRT so that the wiring to the deflection plates is as short as possible.

The clock board I'll either mount in front of the driver and remotely mount the serial port to the rear of the chassis or I'll just use the serial port to secure the clock board to the rear of the chassis.

The power transformer does have a shield over it so there would be minimal interference from the transformer.


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 02, 2018 1:07 am 
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That clock looks very nice, I'm looking forward to seeing how the finished project turns out. I have board around here somewhere that displays a clock on any oscilloscope with an X&Y display option.


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 02, 2018 1:39 am 
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Great project, very cool 8)

Thanks for posting, Tim


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 02, 2018 1:48 am 
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You're welcome.

The 3" CRT clock came about because I wanted one for work and a 5" crt would be too large for my desk.

Now if I should desire to make this a scope again the designer of the CRT driver does make a sweep generator with triggering so I could do that and add a switch to select the clock or scope function.

I am thinking of ac coupling the clock to the driver and figuring a way to have it to where I can flip a switch and reduce the image size. Reason for that is if a round CRT is adjusted to fill the whole screen with the round clock face the square things such as the menu, terminal and binary clock go off the screen slightly. Thinking I could just use the switch to short across a pot in series with the size pot which would allow me to set the size.

The problem is the driver circuit was designed for the dutchtronix clock and it's dc output so that the burn in protection would work and at least with a 5" crt the driver transistor stage didn't play well without the dc offset out of the op-amp due to the dc from the clock board.

But I will try it and see if i can get it optimized for AC coupling as it will be much easier than having to adjust gain and position pots every time I switch to a square screen.

EDIT:

When I ordered the parts I went to order a DS32KHZ TCXO and the through hole version was not available so for now ill use the XTAL that comes with the clock.

The TCXO is more accurate than the XTAL is.

I was torn about using that scope but I realized it would never be useful to me as a scope and was small enough for use at work.

I have a Dumont and supreme that use the 3AP1 which are even less useful to me as scopes but they are too big for work and would require mods for a better crt as the socket serves as the rear support.


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 Post subject: Re: Scope clock
PostPosted: Jun Mon 11, 2018 11:29 am 
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I've got the parts to build the CRT driver.

So I will put it together today and get it ready for the clock circuit when it comes in the mail.


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 Post subject: Re: Scope clock
PostPosted: Jun Wed 13, 2018 2:58 pm 
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Ok I got it wired up per this circuit except the 2.2uF and 1uF caps are 22uF in order to ensure there's no ripple voltage on the B- supply. Used a 100uF cap for the 10uF cap to ensure there's no ripple on the B+ supply.


Image

http://electronixandmore.com/projects/s ... index.html

I found that the voltages listed on the side of the transformer must be the loaded voltages as they all are a little higher than what they should be.

I backed down the variac until the B+ winding was 235Vac.

I do not have the deflection circuitry connected just yet and the deflection plates are conencted to the B+ voltage.

Problem is I barely have any intensity or focus control and other than a wiring error I don't quite understand why.

I'll try conencting the focus and intensity pots in series and seeing what I get after verifying the wiring.


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 Post subject: Re: Scope clock
PostPosted: Jun Wed 13, 2018 3:19 pm 
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Hi

A1 and A2 location wise are reversed in your schematic. Maybe they are also reversed in the circuit?

I normally connect focus and intensity controls in series, with intensity more negative. You show them in parallel. This should operate ok but controls might be near end of adjustment?

Be sure you have enough voltage across the CRT. Too low and it will be dim.

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 Post subject: Re: Scope clock
PostPosted: Jun Wed 13, 2018 6:27 pm 
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I had goofed and forgot to solder the wire from the intensity and focus pots to ground :oops:

It then worked ok, but I didn't like the very wide range of focus (way wider than it ever should be) nor the sensitivity of the intensity control (only usable over 1/4 its rotation) so I wired them in series like this.

The 1 meg between the focus control and ground puts it more in the corect range. The neon lamp also helps put the focus control in its range along with providing a pilot light.

The zener across the intensity pot makes it work over the full range.

I could get a little better control at the upper end if I used a 100K pot and somewhere between a 60-100 volt zener, but this works good enough.

Attachment:
controls.png
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I now have great intensity control and can focus a sharp bright spot.

B- is around -650Vdc.

My only question is when I load B+ down with the deflection circuitry will that be enough load to drop the AC voltages down some.

If it is not then I may try using a resistor in series with the primary to get the CRT heater to 6.3Vac as it is at 7Vac now with B- at -900 something volts and B+ at 410 volts if I run full line voltage to the power transformer.

Having B- at 850 Vdc wouldn't be a problem.

it's the 410 volts B+ that is a problem as it exceeds the transistors rating.



EDIT:

Here's some voltages.

For a primary voltage of 72.6Vrms I get
4.28Vrms on the CRT heater
300Vdc B+
B- is somewhere between -600 and -700Vdc. Not sure of its absolute value as I don't have my HV probe handy and my DMM loads the HV down some.

Think I made a mistake using the 22uF caps as B- takes quite some time to drain down.

Now I have three options.

1. Use a resistor in series with the B+ and one for B- then run the transformer on 120Vac and insert a resistor in series with the CRT heater if necessary.

2. Use a resistor in series with the power transformer so that the primary voltage is 72.6Vac for a 120Vac input which will make the transformer last a lot longer.

3. Do #1 except use lower value resistors and add a zener to the B+ and B- which would provide regulated voltages. The problem then becomes the B- which initially would be slightly over -900Vdc which will exceed the cap ratings.

4. Reduce the 22uF cap in series with the transformer winding to a lower value to reduce B- then do 3.

My thought is #2 as the CRT does work decently far as intensity and focus goes with only a heater voltage of 4.28Vrms and the lower primary voltage will make the transformer run much cooler, but what do y'all think I should do?

EDIT 2:

Here's Here's picture of where the clock board will go. Got it temporarily installed with whatever screws I had but will be using the proper standoffs and screws.

I'm going to make it to where the side panel can be easily flipped down so I can access the serial port when necessary.

Since this will be used at work I won't need the serial port unless to update the firmware which I would do at home.

I am thinking I have a bayonet based neon lamp which will fit in the original pilot light holder so that way I have a proper pilot light while getting the focus control proper.

Attachment:
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EDIT 3:

Didn't have the correct lamp, but I did have a NE-2 that had long enough leads so I could set it inside the socket and solder it to the terminals on the socket base where the wiring normally connects.


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 16, 2018 12:46 am 
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The resistor in the primary didn't work as well as I had hoped. It did drop the voltage but as the load changed with the varying of the position pots the primary voltage varied as well. Can't have that.

So I'll try a 6.8K resistor and 22uF cap for the B+ and a voltage divider for the B- and I will lower the primary transformer voltage to 110Vac.

That should work fine.


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 16, 2018 2:42 am 
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I think that clock is quite neat.

- Leigh

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Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Scope clock
PostPosted: Jun Sat 16, 2018 4:26 am 
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Thanks.

It's also a way to repurpose a scope that isn't really all that good for everyday use.

I'll post pictures when the scope is finished.



EDIT:

Made some progress.

Had a too high B+ issue and I think I might have solved it somewhat using a 16.8K resistor between the first filter cap and second filter cap.

I can now raise the primary voltage to 93.52Vac

Here's what I get.

5.5Vac CRT heater voltage
5.5Vac for the +/- 5Vdc supply
380.4Vdc main B+
299.8Vdc B+

The image displayed is quite noisy due to using clip leads to connect the older clock board.

Seems to be ok other than that.

Running that clock board (Sparkfun version of the Dutchtronix clock) on the +5 volt rail dropped the 5 volts down to 4.89Vdc which is not good.

So I'll either need a voltage doubler to power the clock board from the winding used for the 5 volt supply or I need to increase the voltage on that winding.


EDIT 2:

So I am thinking that perhaps I'll try the zener idea for regulating the B+ voltage.

That way I can get the line voltage up high enough to where the clock circuit can run on the +5 volt supply.

The B- voltage I am not sure what I'll do with it yet.

I do have the original dual .5uF 1KV cap from the scope which filtered the B- so I'm thinking perhaps I'll use it for filtering the B- supply. I can then use zeners to regulate the voltage if so desired.

I'll need at least another .5uF 500V cap though.

That said I could do the type of voltage doubler that uses just two diodes and two caps which would give me a B- of -1.369 KVdc using the original 130Vac winding for the B- which is in series with oen of the 135 volt windings.The B- is based on the unloaded transformer voltages of 346Vac and 138 Vac I could then use a series resistor and zeners to regulate it to -1KVdc if necessary.

Now depending on the deflection sensitivity at the increased B- voltage I might need to optimize the deflection amp for the highest output possible like I did for the other clock using the 5DEP1.

Not sure yet if I will need any compensation.


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 Post subject: Re: Scope clock
PostPosted: Jun Tue 19, 2018 3:30 pm 
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Decided to check and the type of voltage doubler I was talking about I cannot do because of how the transformer windings are connected.

So I will leave the doubler as is, but will switch to 1.6KV caps.


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 Post subject: Re: Scope clock
PostPosted: Jun Fri 22, 2018 5:07 am 
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The clock was running a little fast so I checked and the oscillator frequency is 32.774KHz so I tried to use the RTCTRIM connection on the clock board, but couldn't get a cap to bring the frequency down to 32.768KHz.

I then remembered I had a defunct nixie clock with a RTC so I pulled the XTAL from it and it is 32.771KHZ. I was then able to use a cap to get it right.

Will finish mounting the cap tomorrow then tweak it for 32.768KHz and see how stable it is throughout the day.

I would use the same DS32KHZ TCXO that I used in the other scope clock, but the DIP version is no longer available and I can only get the SMT one.

Now there is a spot for a SMT chip for an optional USB connection (does what a USB to serial cable does) but I'm not sure what pins connect where so i couldn't use that for the chip.



EDIT:

I tried the 1.5-20pF cap and it with a parallel fixed cap was just enough to get the xtal at 32.768 KHz but there weas no further adjustment above 32.768KHz so I tried an 8-60pF trimmer I had without the parallel cap. That worked much better and I have an adjustment range of at least 1Hz above and below 32.768KHz.

I also tested it with B+ removed and the RTC running on the battery backup. Still 32.768KHz.

I found that to get an output on the RTCCAL terminal the microcontroller either has to be removed or I could briefly touch the RTCTRIM terminal. I chose to remove the microcontroller given I didn't think touching the RTCTRIM pin was a proper way to do it plus I didn't want the microcontroller accessing the RTC.

I found that an HP frequency counter was a bit too jumpy with it displaying down to .01Hz, but an HP selective level meter which displays down to .1Hz semed to be more stable far as the frequency counter function is concerned. I just used a scope probe to connect to the RTCCAL terminal.

Once I got things adjusted I still wanted to monitor the frequency so I used a trick that I use with my part 15 transmitter when I want to see the transmitted waveforrm. I laid the scope probe near the wire going to the trimmer cap ftom the XTAL and it picked up enough of the signal to give a -89dBm signal as shown on the selective level meter when connected to the BNC jack and high impedance is selected.

I then set the clock to the quartz clock I have hanging on the wall at work and will see how close the scope clock is at the end of the day. Then I'll check it Monday after its been powered off all weekend to see how close it is.

Now when I had that nixie clock running the XTAL came from it would either lose or gain time (forget which) for the first year then all the sudden it was nearly always correct to the minute.

Once I am sure the clock is right I'll test fit it and see how close the trimmer cap comes to anything in the scope. I did make the adjustment screw be the grounded side of the cap so that I could use a regular small metal screwdriver for adjustment without affecting the frequency.

The zeners came in today.

I've got some hot stuff going on at work right now so I won't get to the zeners for awhile. I'm hoping those 100 volt 5 watt zeners won't get to hot regulating the B+ to 300 volts.

I screwed up and only ordered four 200 volt zeners so it looks like I may keep the 22uF 450V caps or I might switch them out with 2.2uF caps. That will mean I'll need a resistor in the primary side of the transformer so that B- doesn't go over -900Vdc unless it is possible to install a resistor after the first cap that feeds both diodes to serve as a dropping resistor then putting the zeners across the 22uF caps. I could then eliminate the 1 meg resistor across each 22uF cap that is used to ensure both caps have equal voltage on them as the zeners would ensure there's 400Vdc on each 22uF cap.

EDIT:

What I might do is put the zeners across the 22uF caps then I'll insert a resistor in series with the transformer connection to the first cap of the doubler. That way the voltage on the 22uF caps will not go over -450Vdc each.

I'll then adjust the primary voltage to where B+ on the first filter cap is under 450Vd with either a 6.8K or 10K series resistor then the three 100 volt zeners in series across a 22uF cap.

If the CRT heater voltage is greater than 6.3Vac I'll add a series resistor to drop it down some.

I figure the power transformer will generate next to no heat being so lightly loaded.


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 Post subject: Re: Scope clock
PostPosted: Jun Fri 29, 2018 11:18 pm 
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Decided to do it right and order the correct lower value caps.

Got three .22uF 1KV film caps plus two HV diodes like the diodes I used in the other scope clock.

The plan is to run the power transformer on whatever primary voltage produces no more than 400Vdc B+ which will be regulated by zeners after a resistor to 300Vdc.

Now if the zeners get too hot I'll have to figure something else out for the B+.

That should keep me under -1KV B- which will be regulated to -800Vdc by zeners after a resistor.

Once I get the power supply right I'll see what if any geometry corrections need to be made.

If I need corrections I'll do it with variable caps like I did with the other clock.


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 Post subject: Re: Scope clock
PostPosted: Jul Thu 12, 2018 12:09 pm 
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The caps and diodes are in.

Will install them today and select whatever resistor between the first and second B- filter caps gives 800Vdc over a voltage range of 110-120Vac input with the transformer primary voltage being reduced somewhat to keep the B+ on the first filter cap under 450Vdc.

Since it had two fuse holders and I cannot find both fuse holder caps I ordered a new fuse holder.

I will remove the caps for the B- from the power supply baord and epoxy the .22uF caps to the chassis like I did in the other scope clock along with the diodes, zeners and resistor being mounted to the caps. I'll just make a break in the B- line from the board and move the wire to the transformer HV secondary then use that to feed the B- supply then feed the rest of the CRT circuit.

I'm hoping that the three 100 volt zeners for the B+ supply do not get too hot.

Now with how sensitive the selective level meter is I'm hoping that once the clock is assembled fully I can insert the scope probe tip in one of the vent holes near the clock board and get a proper reading as I want to be sure the frequency stays at 32.768KHz when the clock is running. Given how little heat is produced it shouldn't be an issue, but I have to be sure.

Once I get the B- done I'll test the retrace blanking and see if that works ok. If it doesn't then I'll just do without like the other clock.


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 Post subject: Re: Scope clock
PostPosted: Jul Sun 15, 2018 4:26 am 
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I'm just about done with the clock.

Got it adjusted to produce a good image today.

Was lucky in that I could get the necessary compensation for a good image with fixed capacitors given I don't have the necessary variable caps nor do I have a good place to mount them.

The image quality is very acceptable.



Not sure why but when the green led would turn on the B+ would drop from 4.99Vdc to 4.98Vdc and I'd notice a slight image shift.

Fixed it by putting a 30K resistor in series with the LED. It is still plenty bright enough. Was way too bright with its original resistor. I also put in a larger series resistor for the red power led as it doesnt need to be near as bright as it was.

I mounted the variable resistor that is in series with the primary in an existing unused control mounting hole as that's the only place I had for it. The resistor is set to produce 105Vac for an input of 120Vac and the B+ and B- stays regulated at least down to 110 Vac input which will cover any line variation.

The power transformer runs very cool.

Now I just need to find where I put the left side panel then secure the boards to the bottom with double side tape and I'm done.

I gotta work out the retrace blanking though as it doesn't seem to want to blank just the retrace lines and does pretty much what it did with the other scope clock.

Will need to do some research into retrace blanking circuits to figure what the issue is.

Think it is that the circuit was designed for a B- of around -600Vdc.

I'll post some pictures when I get home tonight.

EDIT:

Here's some pictures.

The retrace lines aren't as bad as this photo shows.

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I'll have to retake this one.

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 Post subject: Re: Scope clock
PostPosted: Jul Mon 16, 2018 12:54 pm 
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Well I tried the clock at work this morning and due to how the CRT is tilter at an angle by design it is a bit hard to see due to the bright fluorescent lighting.

I've tilted the clock so the screen is at a better angle, but it is only good for up close viewing. So I may need to figure out something else for work.

Now what I don't get is the fact that the clock was a little off by around 2 minutes at home. Not sure why as I have no proper way to measure the frequency at home unless I remove the microcontroller chip so the 32.768KHz signal is on the RTC cal test point. I could then adjust the trimmer cap.

It would be easier though to get the DS-32KHz and figure a way to solder it to where the surface mount chip for the optional USB interface would go and just use that.

The DIP version of the DS-32KHz that I have int he 5" version of the scope clock works great and keeps reasonably accurate time. I would love it if the DIP version was still available.

I'm thinking that I can use another 200 volt zener in series or I think I have another 100 volt zener. That will raise the B-

I think the deflection amps have enough output to handle the reduction in deflection sensitivity caused by the B- increase.

Maybe that will solve the slight focus issue and maybe it will actually be bright enough for use at work.


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 Post subject: Re: Scope clock
PostPosted: Jul Thu 19, 2018 12:55 pm 
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I used a 100 volt zener and two 20 volt zeners to get the B- to -940Vdc.

The deflection amps can still fill the screen properly.

I really do need to work on the blanking circuit though.

Makes me wonder if the fact that I had to compensate the deflection amps means the trace isn't precisely at the correct points in the correct time which might be causing some of the stuff intended to be displayed to be blanked due to the lower bandwidth.

Also to get the focus control to where proper focus is near the middle of its rotation I had to add 500K between the grounded end of the focus control and ground.

Schematic shows where I should have a 1 meg there which I put on the schematic and shows no resistor between the NE-2 and focus control, but I have a resistor there.

For the 1 meg it could be that I found it wasn't needed with the initial B- or I needed it and didn't add it.

The other resistor it may be that it was needed, but didn't make the schematic.

I might try the 1 meg instead of the 500K and I'll measure the other resistor's value.


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 Post subject: Re: Scope clock
PostPosted: Jul Tue 31, 2018 2:44 am 
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Well I did some more tweaking and got the clock geometry about as good as I can with the single transistor stage used.

Normal clock face

Attachment:
20180730_205502-600x800.jpg
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Notice the slight geometry issue on that one line? I guess that part is being drawn much faster than the rest. Suppose I could use the firmware with adjustable refresh rate and slow the rate down which might solve that problem or reduce it.

Attachment:
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Clock face with room lighting on. Retrace lines are very hard to see.

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Roman numeral display

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Digital display. The clock focus is fine. The camera focus is not.

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Same focus issue as above picture. Notice that there appears to be a slight bend in the bottom line of text.

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