Discussion in 'Electronics & Electrics' started by davidb2012, May 6, 2012.
the trim pots have 25 turns,there should be a hard stop at each end
On the PCB drawing what is the box on the far left with a backwards Q1 on it?
Thats what i thought but it never stops???
Looking at them i think they make a slight click once their at the end.
that is a mosfet
do you have a multi meter?
yeh somewhere i will dig it out. where should i measure?
So do i need the mosfet as it isn't in my circuit. A mosfet is just a transistor right?
Between pin 1 and ground there is 1.8V but between pin 7 and ground it is 0V. at the LED it is 1.5V but no light???
The batteries are ok at 3V
Hall effect sensor is at between output and ground is 1.5V put a magnet up close goes to 0V turn the magnet round goes to 3V.
Just looking at the specs of this hall effect sensor and it says operating voltage is 4.5V to 6V
I only have 3V input maybe this could be the problem?
the mosfet is for later, for the solinoide, it is similar to a transistor
pin 1 and 7 should never been on at the same time, 1.5 is a bit low, remove the resistance. from the led.
the hall effect seems to be working fine, as the output is changing, also measure the voltage on the led, try to make it go to 0, by adjusting the pots.
with no magnet, the the voltage at pin 3 should be at less voltage at pin 2 and pin 6 should be higher then pin5
The T in MOSFET stands for transistor, so it is a transistor.
ok well some good news. Technically the circuit works. across the LED i have got to 0V then when i introduce a magnet either pole it jumps to 1.5V, when the magnet is removed it goes back to 0V SUCCESS however the LED still doesnt light and i have replaced the last resistor with wire.
One pole of the magnet works at 2.5cm away and one pole works at 9cm away.
Iv just checked the LED doesn't light up with 1.5V direct it needs at least 3V so we do have a working circuit. Now do you think we maybe need more power? If we have to then i suppose we will have to fit it in. Maybe 4AA's or 3AA's what do you think. Also how do we get the distance further as eventually the hall effect sensor will be behind 2mm of PVC.
Oh i tried with that small sensor and it was practically impossible
And I hope you'll be gifting it with a flyback diode before connecting it to a solenoid...
pins 2, 3, 5 and 6 are all 1.5V with and without magnet
i have to get to work ,i can make a pic when i get back about 3 ish
great thanks mate. Dont worry i will sort you out when were done.
The opamp can only output a maximum of supply minus 1.5V ( 3 - 1.5 = 1.5v) , a yellow LED typically has a fwd voltage of 2V so it's never going to light up.
Might need to add FET to the circuit now, or just leave your multimeter hooked up while testing instead. You could just use more batteries , but you should keep it same as its going to be in production
When i attach 3 AA's it lights the LED up. The problem now is how do i get the hall effect sensor to sense from a further distance. The more sensitive sensor is next to impossible to solder legs to it is about the same size as about half a grain of rice. its ridiculous.
Well since its in a working state now, the easiest way to increase your sensitivity is to turn R1 until the light comes on (if you just hear clicks and it doesn't light up you've wond it the wrong way) then slowly wind back until it just turns off.
Then repeat with R2
this should be the max sensitivity you can get out of it.
Remember what I said earlier though, that at max sensitivity whilst it may work it won't be stable. you'll need a bit of headroom to cover factors like temperature, drift, being triggered by a passing car (exageration) etc
Maybe I could use multiple hall effect sensors all in parallel that would then give a better rate of detection from different angles. Would it work? seems to me it would.