PNP transistors should be fine. Don't think you ever mentioned the current needed, but it should be low if you're just shorting a switch input

300mA ground pulse is more than sufficient to activate my LED controller.

Don't use rectifier diodes; the forward voltage drop is too high to protect the diode in the one shots.

You are saying that all the diodes in the circuit should be schottky diodes, EXCEPT the first diode that supplies the 12v to the circuit. I spec out schottky diode STPS0520Z for the circuit.

You should use a TVS diode instead of a zener and put a fuse upstream of the diode.

Hows this TVS diode ... ESDH12VD1-TP
https://www.digikey.com/product-det...-co/ESDH12VD1-TP/ESDH12VD1-TPMSDKR-ND/6004875

Thank you
TONY

 

A 18v 1W Zener would be good

Ok .. 1 watt ... Gotcha ... You originally said 1 Amp

You would need to allow the PNP transistor to drive the Leds as well.

LEDs driven by the transistor, not by the IC. Understood.

Thank you
TONY

 

I used 1N4004 diodes in a surge capacity for years with no real issues.

They won't provide any protection to the one shots because the forward voltage is higher than the diode you're trying to protect.

 

300mA ground pulse is more than sufficient to activate my LED controller.

Guessing could cause you to over design the circuit.

You are saying that all the diodes in the circuit should be schottky diodes, EXCEPT the first diode that supplies the 12v to the circuit. I spec out schottky diode STPS0520Z for the circuit.

Any diode would be better than a rectifier diode.

Hows this TVS diode ... ESDH12VD1-TP
https://www.digikey.com/product-det...-co/ESDH12VD1-TP/ESDH12VD1-TPMSDKR-ND/6004875

Won't work. The stand off voltage is too low. When the vehicle is operating, the voltage will be around 13.8V.

Digikey prices tend to be high. They have a wide variety of parts, and I hear they have inexpensive shipping options, but that convenience comes with higher prices.

 

Sorry for being absent for a long time. Can you please remind me this: you need to double the frequency or you need 2 pulses out subsequently, with the same frequency? Is this all you need from this circuit?

I intend to carry an optimisation on your circuit. I do not have much time to read all the posts.

 

Guessing could cause you to over design the circuit.

How would I find the true answer out? ... I do not have the LED controller schematic to look at. ... Is there a way to limited the mA to the On and Off circuits of the LED controller ... And see at what mA the LED controller responds.

TONY

 

How would I find the true answer out? ... I do not have the LED controller schematic to look at. ... Is there a way to limited the mA to the On and Off circuits of the LED controller ... And see at what mA the LED controller responds.

TONY

As a test, you could measure with an ammeter. Set the meter to read max current, then connect ammeter +Terminal to the mcu input and ground the -terminal. If no reading, slowly reduce the scale till you get a reading. A digital auto-scaling meter would be easier.

eT

 

How would I find the true answer out? ... I do not have the LED controller schematic to look at.

You could determine experimentally by inserting a small value resistor (around 10 ohms) in series with the switch. Close the switch to ground the input and measure the voltage across the resistor. If the voltage is too low to measure, the current required in the switch will be low.

Or you could determine the minimum current in the transistor switches you're using that will trigger the device.

I don't recommend measuring the current directly. Resistance is likely to be in the 200-1000 ohm range; with the highest resistance on the lowest range (200uA).

 

As a test, you could measure with an ammeter. Set the meter to read max current, then connect ammeter +Terminal to the mcu input and ground the -terminal. If no reading, slowly reduce the scale till you get a reading. A digital auto-scaling meter would be easier.

eT

That's right ... the LED controller will only draw the amperage it needs to activate. Good Call!

TONY

 

After doing a quick test using the voltmeter. It appears to pull 910 mA to activate. Much more than I thought. See attach photo of my meter reading.

TONY

 

It appears to pull 910 mA to activate. Much more than I thought. See attach photo of my meter reading.

Looks like 0.91mA to me...

 

Looks like 0.91mA to me...

I first thought that too ... Until I looked in the upper right hand corner of the display. It says 00.9 A ... Of course I may be completely wrong. It's my uncles benchtop meter. I am used to my 73 series hand held fluke.

TONY

 

I first thought that too ... Until I looked in the upper right hand corner of the display. It says 00.9 A ... Of course I may be completely wrong. It's my uncles benchtop meter. I am used to my 73 series hand held fluke.

TONY

hmmm...that’s a lot of current. I would’ve thought it would be more like what dl324 mentioned..can you confirm with your Fluke?

 

After doing a quick test using the voltmeter. It appears to pull 910 mA to activate. Much more than I thought. See attach photo of my meter reading.

TONY

Oops...wait. Didn’t see the image on your post.

Looks to me it’s displaying 0.91 milliamperes ....(or 910 microamps)..that’s more like it

 

I first thought that too ... Until I looked in the upper right hand corner of the display. It says 00.9 A ... Of course I may be completely wrong. It's my uncles benchtop meter. I am used to my 73 series hand held fluke.

The meter range is set to mA, so the reading on the main part of the display is in mA. I can't read the upper right portion of the display.

 

Oops...wait. Didn’t see the image on your post.

Looks to me it’s displaying 0.91 milliamperes ....(or 910 microamps)..that’s more like it

The meter range is set to mA, so the reading on the main part of the display is in mA. I can't read the upper right portion of the display.

It .91 mA than. Sweet!! .. So what does this mean for the circuit? .. Everything is still ok?

TONY

 

It means you

It .91 mA than. Sweet!! .. So what does this mean for the circuit? .. Everything is still ok?

TONY

Yes...all ok.
But it means you can simplify the Interface between the circuit and the MCU. you might not need a transistor interface anymore.

If you still want LED indicators remember you only have about 4 ma to play with or you’ll need to put transistors back in.

Good job !

 

We need another measurement.
Measure the voltage at the input Of the mcu.
Without the button pressed and report back

 

We need another measurement.
Measure the voltage at the input Of the mcu.
Without the button pressed and report back

I misspoke. It's NOT a MCU, it is a PIC chip that controls the LED controller. My bad. The voltage at the PIC chip is a steady 4.95V. Does NOT change when controller is on or off. There is also a 7805 Voltage reg on-board the LED controller that gives the PIC the 4.95V from 12v.

TONY

 

I misspoke. It's NOT a MCU, it is a PIC chip that controls the LED controller. My bad. The voltage at the PIC chip is a steady 4.95V. Does NOT change when controller is on or off. There is also a 7805 Voltage reg on-board the LED controller that gives the PIC the 4.95V from 12v.

TONY

Hi

Ok...so the input levels are 4.95v and GND.
You’ll need to use NPN transistors (not PNP) to correctly interface to the PB input of the PIC. They can be type 2n2222 or just about any general purpose NPN. The collector will connect to PIC PB input, emitter to GND, base thru resistor to Q output. When Q goes high, the NPN will turn on and short the input pin to GND.

Update:
After thinking about it...NMOS mosfets would be better. The thru hole 2N7000 version
has the same footprint as a 2N2222. See Attached schematic.



eT