Hardware threshold switch for brake vacuum pump

[PaulHeystee]

Hi,
Just got the switch from Johannes. It works great, however, for my Saab 93 I need at least -65 to -75 kPa pressure, the board switches the pump off at -45 pKa.
Quesiton: how can I modify (by replacing a component) the board so it will switch of at a lower pressure?

[johu]

try replacing R1 with a larger value, like 10k or so.

[PaulHeystee]

I tried various resistor values and found that 15 k gives -5 kPa pressure (cutt-off). Max pump pressure is -80 kPa so close enough.
A trimmer on the board would be nice

[Alibro]

I've been sitting on this for a few months now but finally got round to replacing the voltage regulator and caps so hopefully it will be OK.
I haven't tested it yet and it ain't pretty but no shorts.
Apart from the terrible soldering does this look OK?

[johu]

Should do. Meanwhile I added a 16V TVS diode across the 12V input to protect the regulator. You might want to do that.

[Alibro]

Should do. Meanwhile I added a 16V TVS diode across the 12V input to protect the regulator. You might want to do that.

Will do.

[Alibro]

Should do. Meanwhile I added a 16V TVS diode across the 12V input to protect the regulator. You might want to do that.

I've just spent a while looking for a 16V TVS diode and am now a bit confused at the choice.
I take it the 16V refers to the max reverse voltage?
Would something like this be suitable?
https://cpc.farnell.com/multicomp-pro/p ... dp/SC18689

[johu]

Yes

[Alibro]

I'm having a few issues with the voltage regulator I installed as in I've replaced it a couple of times and it keeps going pop.
The component I ended up ordering was RAG117-5 as it came up as compatible but I can't find any info for it so I don't know if it is the correct part or not but suspect the pinouts are not correct.
After a bit more checking I'm even more confused though as all the voltage regulators I found when searching for NCP1117-5.0 (Replacment part suggested by Johu) have pin 1 as Gnd, pin 2 as output and pin 3 as input, and as far as I can see reading the circuit Johu has pin 1 - input, pin 2 is ground and pin 3 is output.
Can someone please advise where I'm going wrong.
Thanks

[Alibro]

So I've confirmed something but still very confused.
When buying the voltage regulators I bought 10 as they were cheap, so to confirm the pinouts I soldered wires to a spare one and applied 12V to see what would happen. When I connected it as below I got a steady 5V

So if this is correct then I must be reading the circuit diagram on page one wrong because I cannot see how this component would work in the circuit.

Can someone please advise where I am going wrong. I even thought about making my own 5V supply for the sensor but am unsure how this would affect things.

[Alibro]

So to see what would happen I decided to make a small daughter board for the 5V regulator and 2 caps and solder it in with the pins going where I think they should.
If you look carefully you can also see where I messed up the board by replacing the voltage regulator too many times and had to use a link wire.

And the good news is it now works. The bad news is I'm still confused about the circuit.
the worse news is I only get one press of the brake before the pump starts again.
I'm using a very small lead acid battery so that may be the reason or maybe I need to reconnect the vac hoses differently but the main thing is it works.

[johu]

Seems you have the version without the TVS for protecting the regulator.

Otherwise the PCB design has pin 1 as GND, pin 2 (and the tab) as output and pin 3 as input.

[Alibro]

Seems you have the version without the TVS for protecting the regulator.

Otherwise the PCB design has pin 1 as GND, pin 2 (and the tab) as output and pin 3 as input.

I think I got version 1.0
I was trying to get it working before putting the TVS diode in.
This is the same as mine.

Unless I'm not seeing it properly, in this PCB pin 1 is 12V, pin 2 is ground and pin 3 is output?