Constant current / constant volt PSU

The PCB is the standard XL4015 CC/CV board; usually it has 2 pots and 3 LEDs and sold as a li-ion charger, but there is a variant with just 2 pots. I've been using it to charge batteries and as a general lab supply for low current stuff.  It's tiny, even with the displays, but I knew it was only a matter of time before some crap on the bench shorted it out, or wires fell off.
I use it with an old 18V/5A laptop supply which is way in excess of the output power, put it means I can get to 14V ok for charging. 
I didn't need the LEDs, so I removed them and re-used the spare 1/2 of the LM358 to make a x20 DC amp for the current display.

The chip is good for 5A, but the op-amp isn't rail to rail, so current limit wont go much beyond 4.5A; the display won't read above 3.7A.  This would be an easy fix using something like LMV358. Wish I'd spotted that before removing it to modify the pcb.

I got instability on the output as the main cap is before the shunt (on the -ve rail) A 100/25 fixed this, but means the output is now limited to 25V. 

There is a biased switch to allow the current limit to be easily set, rather than starting high and winding the limit down.  Going the other way won't allow most gear to actually start.

The chip is quite efficient - say 80-90%, but it does run warm with a high input to ouput volts ratio with a few amps.  A copper tab was soldered on to the regulator to get the heat to the case. Don't be temped to put on a heatsink; it would do very little in such a large volume and fail to convect.




The case is 80 x 55 x 25.  It's a bit tight and you can see the input terminals have gone and 1 cap is on its side, out of the way. The displays are just the cheapo 70p ones off ebay, modified to improve accuracy - see other blog posts, hot glued in place.  I'd have preferred to mount them under a clear window, but I already had the box.

Boot heaters

Carpet/flat cat 5 used to run from the heater to the connector on the cuff.
This is the amount of insulation to remove allowing it to pass through the barrel connector; it is rubberised, but not very compliant. There are exposed cores after the case if screwed on.  Heatshrink required to cover the gap.





Routing on the sole

Joint on to the heater






6 x 100R 1/2W resistors, carefully soldered onto stranded wire. Solid wire has historically hardened and failed very quickly

4/12/19 Both 0V wires failed where they pass through each insole. Used a longer piece of stranded wire to solder between 2 resistors in case the solder had wicked and the wire work hardened.

Battery pack is an old Dell 3s2p pack

1/12/24   3s BAK N18650CL-29 2.9Ah in heatshrink with protection. https://bestpiles.fr/ Much lighter!

Hacking LED voltmeters

These LED voltmeters are cheaper than the 7 segment modules!



They come scaled typically 0-100V. The linearity is awful below ~1.0 and accuracy is around 10% above 1 and -10% down to 0.5 when it's around -20% These particular ones have had the part number taken off the microcontroller, but it's a safe bet they have a 10 bit ADC to cover the wide voltage range.  One nice feature of these is that they autoscale below 10V, so you get 9.99V then above that 10.1V up to 99.9V. The resolution +/-0.03V (0.02 on 1 module I have), so below 10V don't expect too much. Some modules out there only have 1dp and right justify the display.


I've marked the signal path from the yellow input wire. Basically it goes through the 22k pot, through a 20k 1% (marked 30C), then a 3k9 (marked 58B) to the adc input and also to a 1k (marked 01B) to 0V.
Or to put it another way, there is a potential divider of 23.9k of fixed resistance and a 20k pot in series, and a 1k to 0V. Assuming the pot is mid-position, the ADC input is therefore Vin (1/1+11+20+3.9) or ~0.0278 or (1/35.9)
I needed a 0-5V input to read 0-15 ish. A 18k across the 20k & 3k9 achieved this.
The basic accuracy at low inputs can be improved at the expense of having the meter flicking from 0.00 to 0.02 with no input.  For the above mod, a 1M resistor from pin 5 to 8 (+3v3) means it reads with less than 1% error to at least 4.0 (didn't test above that)
For an unmodified meter, a 1M5 does the same to 12V (didn't test above that)

These Zamberlan boots were made to fall apart

I don't know what it is about modern materials, but they ain't like they used to be.
A few months ago, my leather Zamberlan boots fell apart. The sole just fell off, revealing a crumbling inner core.  It turns out the sole/core is polyurethane/EVA and the cheaper the boots, the worse the life. Whilst I could get the leather parts removed and a new sole glued on, I've just decided to change brands. Annoyingly, the summer boots I bought in the USA for about €10 over 15 years ago have also failed on the sole. They just sell junk there (in case you are an American reading this, that bit is ironic. Just that bit you understand)
I've gone for a synthetic mountain high boot, 4 hour water proof, semi flexible. Quechua (own) brand for €69.  The branded ones wanted twice the money and then more if I wanted the convenience of dry feet. Didn't see any leather boots. Prices went to €180.
Whilst taking off my trainers (well, light hiking shoes) I noticed the heal is coming away from the outer.  I really splashed out on the cheapest pair of similar shoes for a staggering €13.

LS2 FF396 bike helmet visor repair

On the bottom of the lid, there is a control to drop the sun visor down and up.  There are 2 bits. A substantial red semi-circle and a crappy little black lever on a T stem about 2mm x 2mm. Put the lid on a shelf (who doesn't) and eventually you catch this little lever and it snaps off. You then can't retract the sun visor without forcing it.

The mechanism is easy to remove - 2 screws on the outside of the lid behind a rubber trim.
In the pic above, you can just see where the lever has sheared off - look for the arrow.
I found a bit of small pvc tubing, heated it up and pushed over the remaining stub. Then I hot glued it and put a cross pin in for good measure.

The next time it's caught I think that it will destroy the rest of the flimsy mechanism.

It's a real shame on otherwise a very comfy lid. I bought this April 2016. I notice 7 months later the control for the sun visor is up by your ear.

Waitrose email 'service'

I'm really not sure how to start this rant.  Waitrose and John Lewis sell the idea that they are a bit better than everyone else.  And I'd say that was the case until today.
When you sign up with Waitrose broadband, you get an email address. Having had this  a few years, the spam level received was getting to around 10 / day.  I checked on the web app and found the spam filter was off.  Turning it on made no difference. There were rules to set up so I set up the handful of spammer's email addresses to divert to the bin, but that didn't work either.
I contacted support and after a few days they told me it was working fine as there was spam in the junk folder. Spam I'd put there. So back to support and 2 replies and 1 week later I was told to use the John Lewis web app. So I did this and got server errors returned when reporting spam, and the spam kept coming.
So I contacted support and they finally told me that the Waitrose mail server is very old and doesn't work for spam and filtering and the John Lewis web app doesn't work for Waitrose customers.
So, to summarise, about 5 hours work over the 2 weeks it took them to reply finally made them admit that they have no spam filter. Why they couldn't just tell me this on day 1 is totally beyond me.
Their best suggestion was to get a third party email.  I think I'll just get a new ISP. 

Waitrose Wasters.

Jet wash of deck

Jet washed the deck over the last 3 days.  About 4-5 hours, 600 l of water.