Hello!
In a project I want to use a DFPlayer Mini for a sound effect. Since (if possible) I don't want to use an extra microcontroller I wanted to use the I/O-Mode of the module but still trigger it digitally.

The Play-Function is triggered when a specific pin is pulled to GND through a 33k Resistor. Normally this would happen by pressing a button shortly. I wanted to use a transistor for that and an input signal that switches from 5V to 0V (and stays there). I need to use that signal for other reasons.

I thought of using a resistor and capacitor so that the switch from 5V to 0V results in a short impulse that would trigger a transistor to pull the Pin from the module to ground. But I can't really make it work, I'm still quite new with working with electronics. Any hints on how this would be doable?

Thanks a lot!

 

Version #1:
When the control signal is at 5 volts Q1 is turned ON pulling the junction of C1 and R2 to 0 volts, hence Q2 is OFF.
When the control signal is at 0 volts Q1 is OFF allowing Q2 to briefly turn ON through C1.

 

Hey there! Thanks a lot for your idea! It's already so much better than anything I did. Sadly, so far it does not work and I think I still don't understand something.
For the Transistors I used BC547 (because i had them here) but as far as I know that should not matter too much. The Diode is used (again, because i had it here) is a N4148. Also, since I don't have a 1 uf capacitor, I'm using a 10 uf and 1k resistor as R2.

What I don't understand: Why is the diode there? Since the anode is pulled to ground, there would never flow any current through it, right? Or am I misunderstanding something fundamentally here?

Thanks for the help!

 

The 1N4148 is the correct diode, it is mislabeled on the schematic.
The purpose of the diode is to allow a path for C1 to discharge through when Q1 is ON.
Assuming the circuit is wired correctly it might be the pulse width is too short.
Leave C1 at 10uf and change R2 to 10K.

 

circuit can work without diode, at least here since supply is only 5V. without it Q2 base voltage would get negative voltage close to Vcc value and this could be potentially dangerous for transistor. diodes are cheap and good practice is to keep the Q2 base safe.

so without diode, base voltage goes to -4.3V.


with diode, that voltage is clamped to about 0.7V, regardless what the Vcc is

 

Thanks for the explanations! I think I get the usefullness of the diode now... I tried around with different values for R2 and couldn't get it to work.
The function of the Pin is tied to there being more or less exactly 33k Ohm resistor between the pin and ground when the button is pressed. 21k or 55k give different functions. Could it be that the transistor introduces some resistance that changes the behaviour, so a different functionality is activated? Or maybe none at all?

 

I used BC547

Did you wire your transistor with pin 1 being the collector as per above?
If I had to blindly guess I would have thought pins 1 - 3 to be (1) Emitter, (2) Base, (3) Collector.
If you're not getting it to work as others say it will then something has to be wrong. Easy mistake to make. Confirm the transistor is wired correctly.

 

yep, the transistors are all wired up correctly. Any measurements you would suggest to troubleshoot? I'm running out of ideas. I'll try fiddeling around with the Resistor at the input pin, maybe something works there
Thanks for your help!

 

Thanks for your help!

Do you have a volt meter to test with?

 

Yes I do and have been measuring at different locations and to me it seems fine. (That doesn't mean much) Although it's hard for me to see how long exactly the pulse is.

 

What does the voltage read on the collector of Q2?

 

While the signal is at 5V it reads 3.3, then on the change it falls to about 0.1 and then slowly rises until the control changes again to 5V and it jumps to 3.3V

 

transistor Q2 is open collector... player input is used as pull up circuit. the player is likely using 3.3V which is what you measure. when activated, Q2 goes low (0.1V or so). since it rises slowly after being triggered, most likely there is a filter capacitor at the input of the player. how long it takes to get up to 3V?

 

It takes about 15-20 seconds to get to 3V and really only reaches 3.3V after putting the control to 5V again.

 

While the signal is at 5V it reads 3.3, then on the change it falls to about 0.1 and then slowly rises until the control changes again to 5V and it jumps to 3.3V

The circuit is working, however it might require a more definitive on-off pulse to activate.

 

It takes about 15-20 seconds to get to 3V and really only reaches 3.3V after putting the control to 5V again.

Install a 100K resistor from the base of Q2 to ground.
What values are R2 and C1?

 

i have re-read the original post and looked up that module. now i understand that you want to use analog mode.
https://wiki.dfrobot.com/DFPlayer_Mini_SKU_DFR0299

such as this:


so you want to connect output and GND of suggested circuit in place of button that you are trying to simulate. i think you are trying to use it instead of K4 (pause/play). so GND of described trigger circuit need to connect to player module GND (right side of K4). the output (collector of Q2) need to to to the left side of K4 (to resistor 33k).

 

in this case (analog control), resistor value (R7) is still needed. since transistor is not an ideal switch (it is less ideal than button), it will have some small voltage across C-E when on. so you may need to adjust the resistor value slightly if that becomes a problem. this is easy to test when using trimpot instead of fixed resistor. and by turning it to some other value you can have any of the functions.

 

Install a 100K resistor from the base of Q2 to ground.
What values are R2 and C1?

R2 is 10k Ohms right now and C1 is still at 10uF. Interstingly, if I control the pulse signal with an arduino and make the pulse 0,5 seconds it works with the above circuit (I added the 100K resistor to the base of Q2). So there really seems to be something wrong with the timing off it all. So probably the pulse is too long?

 

Additionally: This does not work with 1k Ohm as R2, so the 0,5 seconds impuls interact with the size of the resistors in some...way.