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General Chat / Re: What did you buy today? Post your latest purchase!
« Last post by Insatman on Today at 08:17:02 PM »
I bought the NewScope LCD replacement kit for my Tek784D recently and installed it today.   Took most of the day, not because of the kit really, but because some idiot working on this unit before me stripped out a couple of screws and left one of them broke off.  Getting them out and re-tapped took quite awhile.  The kit is pretty nice and very well packed.   No instructions included in the box but a pretty decent illustrated manual is on their website.  A few steps were missing but nothing major.  With the floppy drive replaced with one of those USB units the old girl should be with me for awhile longer.   The only downside is the price...$350.   I paid about $450 for the scope last June which is a deal here in Philippines if you can find one at all. 
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Breadboard gone.
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Projects, Designs, and Technical Stuff / Re: DC Motor crashing uController
« Last post by ogden on Today at 08:13:43 PM »
I have a drawer full of 1.5A 7805s that I have been working my way through, but will need to replace them at some point, and might as well bring myself to the 21st century.

Those are not "bad" regulators, you just have to know what they can do or can't. Those will leak all the hi-frequency noise though w/o filtering/regulation. -
 So you must filter high frequencies before regulator. Notice in your waveforms ringing frequency, it's very high. Then check PSRR specs of your regulator and you will see your problem - that your regulator can't regulate/filter such a high frequency noise! Actually even modern LDO's can't ;)

Solution: Do you happen to have some 10uH inductor capable of currents that are needed for 5V rail? Supposedly 100mA for that blue pill shall be more than needed. Put one such inductor and 10 Ohm resistor in series before C2/C7.

High frequency 2vpp pulsations on 5V bus is still *very* bad. You have to get them down to 100mVpp or so.
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1GHz is 35 ps, not 350 ps  :D

lol...I wish...Formula is 1/f x .35 or 1Ghz = 350ps.  Look it up at Tektronix.
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Projects, Designs, and Technical Stuff / Re: UV-C Sensor
« Last post by Hero999 on Today at 08:07:53 PM »
If you put an "UV-bandpass filter" in front of a photodiode (like this for example https://www.ebay.com/itm/UV-Optical-Bandpass-Filter-254BP10-12-5mm-diameter-EB00014T/311641773821?hash=item488f4c16fd:g:WIgAAOSwepJXa~vi) it might be sufficient to decrease the sensitivity to visible light enough, so you can detect the difference in emitted light intensity with a normal photodiode and an transimpendance amplifier. Photodiodes are less sensitive in the UV region, but with your light source, I think you still should be able to detect sufficient UV light, even with the 22% transmittance of the bandpassfilter.
The trouble with that is the photodiode's plastic packaging might be opaque to UV.
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Regarding critics, around here it seems there's a feud against FB, based on the perceived "reality" that engineers don't fall prey to Zuckerman's devices - somewhat disconnected from the reality as a while ago a small voting here at the forum showed (IIRC) about 50% had a FB account. Oh well... Each to its own.

Having a Facebook account and actually using it regularly are two different things. And using it regularly for groups is another thing entirely.
This "reality" among engineers to snub Facebook for such things is very well known in the engineering marketing community.

Just so.

Engineers want to build things that last, not just have an ephemeral "2 weeks and they're gone" lifetime.
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Aiming for < 4V, but since this driver is otherwise perfect I may
need to step up and use a 6 or 12 Volt motor.
Thanks for your suggestion.
Yes, there will be a voltage drop across the driver transistors.

All the ICs suggested so far are not specified to work below 5V, except the L9110. The devices with BJTs have too higher voltage drop, for low supply voltage applications.

How about the DRV8836?
http://www.ti.com/lit/ds/symlink/drv8836.pdf

Is this going to be hand soldered or are you going to use a reflow oven? The DRV8836 has a thermal pad, which can't be hand soldered.

An alternative is the LB1938FA, but it's only one H-bridge.
http://www.onsemi.com/pub/Collateral/ENA2041-D.PDF

The TC78H620FNG is another possibility, which is surface mount, but doesn't have a thermal pad, so is fairly easy to hand solder.
https://toshiba.semicon-storage.com/info/docget.jsp?did=35802&prodName=TC78H620FNG
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I cannot believe that the included probes PP215 200MHz are what the label says due to their poor performance. I have a very old probe (around 27 years old, all labels are long gone due to extensive usage,  I used it when I was an E.E.),   I  also have a couple of P6100  100MHz probes I bought at AliExpress for a different oscope. Today I was probing some signals on 8 bit MCU using the standard probes and did not like the signal shape. So, I decided to compare all those probes and that is what I got (I was mostly paying attention to the rise/fall times)

All probes have been properly calibrated and used in 1:1 mode.

a) 27 year old probe - 20 ns  - yellow trace;
b) P6100  100MHz Chinese probe - 26 ns - blue trace;
c) P215 200Mhz - 33 ns - green trace;

The result speaks for itself.






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RF, Microwave, HAM Radio / Re: 50 Ohm resistors
« Last post by daqq on Today at 07:50:17 PM »
Depending on your requirements, they do exist, and don't cost that much (~0.5 EUR/pc http://ie.farnell.com/vishay/cmf6550r000fkeb/resistor-metal-film-50ohm-1w-1/dp/2419001 ). Or, if you're in a cheap mood, you can go with 2x 25 Ohm in series - it might look better than 2x 100 Ohm in parallel, but with slightly worse inductance.
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General Chat / Re: Maplin "Insurers cast doubt over future of Maplin"
« Last post by trys on Today at 07:45:53 PM »
Maplin have an offer on now where you get a £5 voucher if you order online and collect in store, if you spend more than £10.

That really shows how they are trying to keep liquidity right now.

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