I’ve always thought that resellers allowing purchasers to leave product reviews and feedback was a good idea, and on many occasions I’ve read the reviews and used this to bias my purchasing decisions.
But what happens if the reviews are false, or the company doesn’t actually publish all reviews?
Screwfix in the UK are an example of an excellent supplier who don’t appear to overly sensor their reviews. Yes, they tend to show the more favourable reviews first, but all the reviews are there if you choose to scroll through them and I personally think this works in their favour.
I was looking for a table saw to do a couple of light weight jobs. I could have opted for the cheapest one that was available but after reading the reviews decided that I would spend a few extra pounds on a slightly better model. Win-win… I get a saw that many people seem to feel is adequate for the job, and Screwfix make a bit more money out of me. I’m also a happy buyer now and will return next time I need something. I feel I can trust them.
Unfortunately not all companies are as enlightened, and I’ve now been bitten twice by companies possibly withholding bad reviews, and I know they withhold reviews as they have withheld ones that I’ve written.
I recently bought a wood working lathe. I decided on the model based on the three glowing reviews published about how easy it was to change the spindle speed, and how powerful the motor was. What they didn’t mention was the fact that you needed a socket set to loosen four bolts to change the belt position (changing spindle speed is a common requirement with wood working), and the motor was severely underrated. Also the main components were cheap cast pig iron, poorly finished so didn’t move well.
Needless to say, my less than glowing review didn’t make the list.
I also came foul of this with one of my electronics suppliers when I purchased a cheap-ish RF generator. It boasted a fine adjustment frequency control and ease of range selection. However fine adjustment was impossible as the slightest touch of the cheap single-turn potentiometer caused massive frequency change, and the six band range selector switch, which is actually a twelve way rotary switch without any stops, causes very strange behaviour if one of the unallocated six positions is selected. Apparently this reputable supplier didn’t like these comments either and refused to publish the review.
Not publishing poor reviews is a very silly mistake in my opinion. If I read poor reviews I tend to move up to a more expensive models; I’m a firm believer in you get what you pay for and don’t mind spending a bit extra if it’s going to be decent quality. However, for these suppliers they have damaged their reputation with me. Bottom line… I don’t trust them to tell the whole truth any more.
So, the reseller of the lathe now has their never ending train of marketing Emails automatically consigned to my junk folder, and I refuse to trust my electronics supplier when it comes to expensive items of test equipment.
Read the reviews and then checkout other comparable products being offered by the same supplier. If nobody is ever saying anything bad especially on the cheaper offerings, I’d be suspicious.
Also, check out the reviews for the same product from other suppliers if possible.
I was looking at designing a variable speed controller for the motor on my woodturning lathe. Nothing is ever simple.
Whilst doing some research I came across an article by Kevin Brady who explains in clear and digestible detail, all about Horsepower, watts and amps ratings of AC motors, and the complete pack of lies that some sales and marketing people try to dump on us when it comes to claims about how powerful the motors in their gizmos are.
It's well worth a read.
The battery pack manufacturers are, in my humble opinion, scamming the general public into buying expensive battery packs when they don’t need to.
I’ve a Fujitsu Laptop that I use in spurts. Sometimes it’s in daily use being lugged around with me constantly, other times it gets left on the table under a pile of paperwork and not used for weeks at a time.
Recently I switched it on and the battery was flat and then found that it refused to charge. It’s around four years old so I thought that it had probably just come to the end of its life. The Laptop kept saying it was 98% charged but the charge indicator wasn’t illuminating.
I wondered if perhaps just one of the cells in the pack had failed (and the others could be useful for other things) but then I had a thought; I’ve seen this before with other so called “smart” battery packs. I took out my trusty Dremel power tool and carefully cut into the pack where I suspected the intelligent battery monitoring circuit was.
Once I’d cut into it, I could see the two connections going to the cells and placed a volt meter across them. The pack was reading 9.1v.
I set by bench top PSU to 11v and hooked it directly across the terminals. I applied power for around 5 seconds, removed it, waited a few seconds and repeated a few times. After each cycle I would check the pack voltage and slowly it started to climb. Once I got the pack up to around 10v, I quickly inserted it back into the laptop and switching on the power. Hey presto, after a couple of seconds the charge indicator came on and Windows reported the pack was 4% charged… and charging. I left it charging whilst I got on with other activities keeping a fairly close eye on things (these retched batteries have a habit of catching fire) and after around 90 minutes or so, Windows reported the pack was fully charged and this was confirmed by switching off the mains power and the laptop happily running on its battery pack whilst reporting around 90 minutes of run time available. This is about right for this laptop.
I've got a thing for clocks... I wonder if it's because I'm not getting any younger.
Anyway, I had a day free over the weekend and decided It was clock building time.
There's not much to this clock really. A PIC18F25K22 running some simple firmware written in AMICUS18 BASIC. There's a Dallas DS1302 RTC chip with battery backup, and a handful of other components.
I've been experimenting with different firmware to see which makes the display the most readable.
The image on the left of the clock front is showing a time of 10:20:13UPDATE 29/10/13
I've created a construction project for this clock which can be found here.
Whilst attempting to repair a simple microphone pre-amplifier for a friend, the culprit was found to be a blown transistor. A quick internet search found the specifications of the device and it was then a simple matter to find a suitable replacement from what was available in the junk box.
Interestingly, my friend, who has only a casual interest in electronics, was bemused by all the Vcb, Vce, Ic and other details in the parameter tables.
So I did a quick drawing of a simple common emitter amplifier based on a NPN transistor and explained the different values.
Below is a sample specifications table for some NPN transistors. Notice the three BC107 transistors at the bottom of the list are from two different manufacturers, but their specifications vary quite a bit. For example, the Hfe (Small Signal Gain) of the TRU device is over four times that of the CDIL variant, but the CDIL variant has a higher maximum working frequency.
The parameter that most hobbyists are concerned about tends to be the Ic. This is the maximum current that the transistor can drive when a load is connected between the Collector and +Vcc.