I have assembled my Shine On and Getting to Blinky boards and I really enjoyed the process. All went well and I’m grateful for my magnifying head-set.
Moving on to the CE header project now.
Moving on to the CE header project now.
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My CE Header board is currently on order at Ohspark and I’m working my way through the Sensor Board. I also signed up for the apprenticeship program here and am looking forward to doing the projects.
I’m especially looking forward to the Current Sink or Swim project as I would like to test battery capacity.
I have a collection of old HP calculators that I often rebuild the ni-cad battery packs. I ordered some batteries from China and went to all the trouble of fitting them into the battery carrier pack and found the capacity seemed very low. I know I could do rough tests by using a resistive load but I would like to apply a constant current to get an accurate reading.
Another project I’m thinking about is a device that can turn on my PC via the internet by just shorting the power connection momentarily. This is so I can wake up the PC remotely, allowing me to remote on to it.
I ordered the Analog Discovery 2 with my apprenticeship subscription and just took the $75USD freight charge on the chin. I just received a call from FedEx saying they want to charge me import duties and GST (goods and services tax) on it 
The law here is anything imported that comes to more than $400NZD gets slapped with these duties.
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Submitted my sensor board to Oshpark so I can’t wait to get it back and start building it!
Congrats Gary! It looks like you have some awesome projects lined up. I can’t believe how steep the import duties are where you live!
The AD2 was $15 over the threshold of $400 for the taxes but the actual taxes weren’t too high so it worked out okay. Even with the freight and taxes, it was still cheaper than buying it from Element14 and the like.
The Analog Discovery 2 arrived today which is exciting. I tried out the scope by connecting it to an HP calculator AC adapter which my multimeter measures an output voltage of 12V AC.
When I measure it on the scope I get a reading of +17V to -17V. The only thing I can put that down to so far is my multimeter is reading the RMS value and the scope is not?
Ah, so that’s likely the un-loaded voltage of the transformer inside of the adapter. Those are usually pretty loosely spec’d in the first place (10% of the specified 12V). But transformers’ voltage normally drop when you start to pull current out of them into a regulator.
Correct! I assume the voltage measurements from both the voltmeter and scope were with the same or no load. Such an AC adapter probably has a very low current rating anyway so I would expect very little difference between loaded and unloaded voltage measurements. 12V is indeed the RMS of 17VAC.
Vrms = Vp / √2 = 17 / 1.414 = 12.02 Vrms
or
Vrms = Vp-p / 2√2 = 34 / 2.828 = 12.02 Vrms
Good point good point. Guess we’ll have to ask that Gary tests it out while loaded too now 
I’ll connect the power supply to the charger with battery installed tonight.
I measured the voltage with the multimeter and the scope while the power supply was not under load.
Thanks @1.21Gigawatts - I did the calculation for the 17V peak last night but I didn’t think to calculate the peak to peak.
Here’s a tip if you want to install Waveforms on Fedora workstation. I received an error relating to libc6 v2.14 not installed although the later version of libc6 is already installed.
I got around it by using this command…
sudo rpm --install --nodeps -vh digilent.waveforms_3.7.5.x86_64-2.rpm
Linux Mint wasn’t so hard - just install Adept 2 first (found on same page as Waveform linux download).
Okay - I measured the AC power supply with the battery installed in the charger and the scope reads 12.5V (25V p-p) and the multimeter reads about 9.56V.
I was assuming the discrepancy between the two measuring devices was because the multimeter is a true RMS reading and the scope is not?
If Vrms = Vp / √2 then 12.5/√2 = 8.84.
It doesn’t = 9.56 reading from MM.
Maybe I should crank up the old HP analog scope and see what it reads…
What is the current rating of the AC adapter?
The equation Vp / √2 assumes a perfect sinusoidal waveform. If there is any distortion the meter could give a slightly different reading. Also, with the scope you are looking at one peak whereas the meter is measuring continuously. Any variation in the amplitude of the waveform over time will also result in a discrepancy between the two methods of measurement.
Thanks for the detailed prompt reply.
375mA output at 8V.
The waveform is a little distorted; your explanation makes sense and explains the discrepancy after taking RMS into account.
Correct me if I’m wrong but does this mean that any AC voltage reading taken via a scope should be converted to RMS before doing any other calculations?
Ah, 8V. Looking back at your posts I see you never said it so I must have assumed it was a 12V adapter. And in that case, with an unloaded output voltage so close to it’s rated voltage I also assumed it was a decent quality low current (100ma or so) adapter. But no, it’s just a cheapie. 
No, not necessarily, it depends what you are trying to measure. If you are measuring the RMS output power of an audio amplifier, for example, then yes. In the case of your adapter, both measurements were correct they just represented two different aspects of the waveform. Knowing how they differed allow you to convert one to the other.
My CE Header and Teensy boards turned up yesterday. Installed Arduino IDE and Teensyduino. Just waiting for some more bits and the sensor board to turn up.
In the meantime I have a project where I will be using a teensy to convert an old IBM Model F keyboard so I can use it on a modern PC.
I built the CE Header and the Sensor Board and assembled them a few weeks ago and here’s the result. I’m still waiting for the “grabby things”, hence the bodge in for the probes.
All working fine albeit for the LED intensity is quite low because of the wrong resistors installed. They were the only ones I had on hand. I have ordered some 56ohm ones which I think will drive the LEDs properly.
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