Help with 555 device and interfacing with another device

[Boguita]

Please show a drawing of what you did...
A picture is worth a thousand words
Can you measure voltages with a DVM?

Ok! I've made some top notch drawings!!
And yes i can measure voltages with a DVM if by that you mean a digital multimeter. I have some Uni-T UT71. I've been doing it. But i don't trust myself measuring Amps. I know how to do it but i rather no because it's easier to not know what i am doing and damage something.

I've been testing (moon shooting actually) some different things in the meanwhile and i'll explain each one of them by drawings. I'll call them scenarios.
Please consider that powering the LED like you taught me works with no problems.


This is the first scenario. For this little guy i have Current ratings for typical and max consumption. 20mA is for idle and 55mA is typical load. This is the 555 device i had that i was using before your transistor solution.
Since 20mA for idle is about the same as the LED switch light i thought at least i could have some response from the device replacing the led that i can make work with the transistor for the circuit board.
Failed! Even if i did manage to do it i used Falstad's circuit simulator and i with realised that i won't be able to give more than about 30mA to the collector because base voltage is too low. Am i right? Also used this calculator: http://www.petervis.com/GCSE_Design...ator/transistor_base_resistor_calculator.html
For 55mA of Icolector i would need to replace my R1 for 68.66ohm resistor. Then i would go to falstad's simulator and the thing did not got as i expected, Ic was never higher than 29mA.

Scenario2:

The manual for this one doesn't talk about amp consumption. I would really like to use this device because i can trigger it with delay.
If i turn the hotspot manually on at the same time that charging starts taking place, it won't boot and it go in to charging mode. So for all of this to work nicely it should be: first i turn the hotspot on via switch. 1,8v is present, starts the p8015(device above) that's programmed to delay triggering via relay for the charging device in the amount of time i want, say 10 seconds. When i power the hotspot off, 1,8v stops being present and the p8015 goes off, and so the charger.
It didn't work. and since there's that diode bridge on the input i think that ground doesn't behave like ground on the socket i was plugging in.
I guess this board should need more amps than the previous scenario, so i quickly gave up and thought of another thing:

Scn3:

So i would only need to trigger it and i should be fine to accomplish what i need. This is my preferred solution because i don't have to worry about powering requirements from the device. But not so easy as it seems
I used the DVM on the "pushbutton" socket and where on i wrote +11v on the drawing it's actually not very accurate as sometimes it reads about +10v, and i've probed with the DVM´s negative lead on the other pushbutton socket. I figured i could make the transistor sink that current but i didn't manage to trigger it. Don't know why! this is really what i need.

scn4 on the desperate side:

well this guy is rather small and i searched the datasheet online. Couldn't be sure that the data was for this exact brand but i guess ratings should be similar and i suppose it needs 37,5mA for activation. more than what i guess i have according to my simulations.
i was trying to replicate this :

which is everywhere on the internet and seems so easy when you google "drive a relay through a transistor"
I guess my transistor is ok because i re-tested it with the switch's LED light and it still works like the first time.



Sorry for the ultra long post and many many thanks for your time again.

 

[dorke]

No problem with long post at all.

Driving this rely (which needs about 23mA for activation) should work fine.
In this circuit it will use about 12/400=30mA.
It will give you the greatest freedom to operate "stuff" since it's contacts are "floating" and will emulate a manual switch in the best way.

Please measure the voltage at the 1.8V when it is in charging state and non-charging states.

If we go back to the beginning.
I couldn't understand what actually wont to do.
Could you please explain it clearly?

P.S
when driving relays the risk of damage to the NPN increases,
so you used the diode across it's coil,which is fine.
For more safety(since you connect a valuable device to it), I would use another series blocking diode to prevent damage in case the NPN breaks-down,and lower R1 to 560.
like so:

 

[Boguita]

No problem with long post at all.

Driving this rely (which needs about 23mA for activation) should work fine.
In this circuit it will use about 12/400=30mA.
It will give you the greatest freedom to operate "stuff" since it's contacts are "floating" and will emulate a manual switch in the best way.

Please measure the voltage at the 1.8V when it is in charging state and non-charging states.

If we go back to the beginning.
I couldn't understand what actually wont to do.
Could you please explain it clearly?

P.S
when driving relays the risk of damage to the NPN increases,
so you used the diode across it's coil,which is fine.
For more safety(since you connect a valuable device to it), I would use another series blocking diode to prevent damage in case the NPN breaks-down,and lower R1 to 560.
like so:
View attachment 26041

Hello again! Just read your answer now but in the meanwhile i've managed a way to make it happen:
This is the ideal idea that i've had before but i've analysed the schematics and i thought i could replicate the behaviour of that transistor that is connected to screw02 but "bypass it" with my transistor that's driven by the hotspot. i've soldered collector and emitter both directly to the SW1 on board like how i drew on the picture above, and unlike in the first attempt where i've connected them to screw02 and +12v it's working nicely!
It should do no harm, right?

Answering the question of what i am trying to do:
I have a 451 Smart car and i've exchanged the original radio Head Unit for an ipad mini which is fitted through a 3D printed support i've designed:

I control it (volume + and - , PREV / NEXT and source) with the car's original buttons that you see above. And i also reserved one of them for opening the garage door. Its removable because (beside chances of being robbed) the battery gets dangerously hot if i leave the car parked on a sunny spot.

Then Spotify and GPS is nothing without mobile internet so i've purchased the "hotspot" for having it on the car. The ipad can take the sim card but if you use the hotspot it can relay your mobile phone calls to the ipad, and then i can use bluetooth hands free for taking calls when i'm driving.

That's where the problems you've helped me with came up. The hotspot was the one imposed by the service provider so i didn't have much to work with except for dealing with its "weaknesses" : didn't have a "normal" physical switch for powering on or off, unfortunately does not work without the battery, when it starts charging and the device is off it takes about 30 minutes to boot up when you press the power button and didn't have a pilot light for indicating that it is on.
I had it stored under the seat and had a manual switch for controlling the usb charging and i had to twist myself to power it on and off, and it was not very easy. So i decided to make this gadget.


Here is the switch that controls it all.
The box i've made is under the seat, and right now i can know when the hotspot is on or not because the led lights only when it is on.
I press it (it's momentary) and one timed relay closes contact for the hotspot power switch for about 5 seconds and then releases (what the hotspot takes to accept the on "order"). Then when the 1,8v comes up it triggers the k8015 that's programmed to only close relay contact (for the charger and the switch LED) when triggering signal is present for more than 5 seconds. And it releases contact immediately when 1,8v stops being present, so that when the hotspot powers down it won't loop again into charging mode.

This solution is better than just plugging a relay because if i power on the hotspot and at the same time turn on the charge it will boot into charging mode and repeating the on procedure takes about some 40 seconds.
It may not seem much but when i get into the car and want to go somewhere, waiting that long makes you start driving and then be tempted to control the ipad and that messes up with the practicability of the whole idea.

That said, do you think that what i did there with the transistor and the k8015 is safe?

Thank you again.