Posted on November 14th, 2014 12 comments
Dave investigates two very serious issues with jitter on the Rigol DS1000Z series oscilloscopes, including the DS1104Z and new DS1054Z
Some sort of modulated sampling/trigger jitter problem at 5 microsecond intervals (the “5us jitter problem”). And severe jitter with the AC coupled trigger mode, a problem which is also present on the DS2000 series scopes as well.
NOTE: So many people have been confusing AC trigger coupling with AC input coupling people will be more familiar with. This issue has *nothing* to do with AC input coupling, it is AC trigger coupling!
Posted on November 11th, 2014 23 comments
So I get an Ebay email alert for something on my watch list. An item that rarely comes up, I was excited!, but then comes
SCAM SIGN #1: The seller has zero feedback.
SCAM SIGN #2: The seller is in Mexico. Not to offend any Mexians of course, but it’s not the US or the usual Ebay countries.
SCAM SIGN #3: The item is priced vastly under what the going market rate would be. A “to good to be true price”, and the wording of the seller seems to indicate they know how much this thing is worth. But hey, it’s an auction, they might be relying on bidding frenzy (but how would a normal zero feedback ebayer know this game?)
But hey, ebay and PayPal have an excellent buyer protection system provided you play the game by their rules, so I figured what’s the harm in bidding (the protection (and almost everything o ebay) sucks for sellers, but for buyers it’s a dream).
Turns out quite a few people thought so to, and bidding went from a start of $99 into the 4 digit territory. But still very low for such an item, so clearly everyone was thinking the same thing, but still being cautious that it’s a scam. Otherwise the item would have gone for much much more money I’m sure.
But like I said it’s rare this item comes up, so I was willing to play along with the buyer protection scheme. There was a reasonable chance it could be legit, so I searched for other similar items so see if they ripped off the images or text, but didn’t find anything. And the text in the ad sounded like a legitimate owner who needed to sell. If it was a scam ad, they certainly knew know what they were doing and how to market this thing.
Turns out I won just a little bit under my maximum bid – awesome! Excited! But still knowing there is a very good chance this is a scam…
So I go to pay for the item using PayPal through the usual ebay checkout system to ensure buyer protection.
SCAM SIGN #4: The checkout fails! I get the following error from PayPal:
“This recipient does not accept payments denominated in US Dollars. Please contact the seller and ask him to update his Payment Receiving Preferences to accept this currency.”
At this point of course I know 100% that it is a scam. But I play along anyway just to see how they are going to do it…
I send an innocent message and get a response:
So I reply that it doesn’t work, and I’ve never seen this before etc. Then they send a reply:
And on top of that the item shows up with the familial “Payment Received” icon in my ebay account!
That message and the icon marking is of course confidence trick to make you think ebay ok’d this, when in fact any seller is simply able to mark any item they sell as “Payment Received”
NOTE HOW EBAY WARN YOU AGAINST THIS EXACT THING!
Then I find:
SCAM SIGN #5: I get a manual PayPal invoice in my email inbox. It’s genuine of course, not a fake PayPal site that will steal my login (another variation on the scam!)
So by now it’s clear how this scam works:
- They set up new ebay and payapal accounts
- A really good scammer would hack an existing ebay account, or increase the feedback by buying a ton of 99 cent items from other fake accounts of theirs etc, but this one was content with zero feedback.
- List something exotic but one that would have high demand, and do a really good job with the listing making out they are the owner who needs to sell it because it’s not needed any more.
- Deliberately set up the PayPal account in foreign currency so the (almost certainly US or other major country like Australia) buyers PayPal checkout will fail.
- Make it out they have no idea what’s wrong and that they are sending an invoice manually, and try to convince you that ebay ok’d this.
- Sucker pays the money and they vanish with it. Maybe they might complete the scam by sending you an empty box with tracking number, but they have their money, so they probably won’t bother.
So there you go, ebay scams abound, and this is just one of them, and it’s simply a matter of using some common sense to sniff them out, and following ebays advice and systems.
Don’t get caught up in the excitement of thinking you are getting that bargain or rare item you are after. Some even justify getting scammed by saying “well, I was willing to take the chance at that price”.
Posted on November 10th, 2014 8 comments
Part teardown, part repair, Dave looks at an Australian designed and manufactured Ness D16X alarm panel that has failed.
What’s that smell?
Can it be fixed?
How do you repair solder mask on a PCB?, or add solder mask to your own home etched PCB’s?
And another look at PCB spark gaps.
Previous PCB Spark gap video
Posted on November 7th, 2014 19 comments
Dave yet again debunks Solar (Freaking) Roadways. This time the prototype SolaRoad solar cycleway path installed in Amsterdam in Netherlands.
Dave shows how to go about doing ballpark engineering feasibility calculations for such a project, calculates the expected payback period, and SPOILER, shows why Solar Roadways will never be a viable technology. This time using real measured data from the Netherlands cycleway prototype, and real measured solar insolation data for the Netherlands
SolaRoad Project Website
Solaroads press release
Road Construction Costs
Road network lengths
Average Household Energy Consumption
Price Per Watt for solar panels:
PV System installation costs
Solar Irradiance / Insolation data
Electricity prices for households
Sunpower P18 solar panel Datasheet
Posted on November 4th, 2014 8 comments
How a Microwave Magnatron Works
Isolated USB-RS232 Interface
LGB Model Train Controller & Decoder
Caterpillar Dump Truck Controller
2114 SRAM Memory