Hi,
I need to command a PNP bipolar transistor with a DAC (MCP4725) through a resistor. So a current can enter in the DAC output. It is possible ? Is there a problem with this ?
Thanks in advance for yours responses.
You need a linear amplifier. A single transistor isn't going to work very well, especially if you need to go all the way to down to 0V or all the way up to your power supply voltage.
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Yes there could be many problems with this. Post a schematic, not a frizzy picture along with Arduino and modules you are planning on using. Include links to all hardware items. Define the voltages and currents involved.
Of course. The real question, is it the best way to accomplish what you have in mind. But we don't know what you are trying to do.
Please explain what you are up to.
How did you reach your present conclusion? Any special reason for a PNP in particular?
Thanks for your responses. Of course I can explain. It's about videos games.
I find it unfortunate that video game controllers now incorporate a gyroscope but that many games do not use it. I mostly played on PC with keyboard and mouse and now that I play on console I have trouble aiming with the right stick. So I made a first board based on gyroscope and Arduino : with the "Mouse" library, I made the Arduino acting as a mouse and made the cursor move according to the movement of the gyroscope. It works very well. I tried on PS4 but the mouse are not natively recognized and I had to use an adapter but it's not really effective. So I disassembled my PS4 controller to see how the analog sticks were made and those are simple 10k Ohm potentiometers (two per stick: one for up-down and one for left-right).
So I imagined a scheme to change the voltage at the output of the two potentiometers according to the movement of the gyroscope (see attached file). The stick potentiometers are POT_V and POT_H. Everything is supplied with 3.3V (VALIM_POT). VIN_V is the DAC output for vertical motion and VIN_H is for horizontal motion. VOUT_V and VOUT_H are the voltages that the controller will see on the right stick. I can only use two DACs because the MCP4725 can only take two I2C addresses.
In simulation it seems to work even if the voltages of 0.6v of the transistors bother me a little. The resistances will have to be reworked I think. What do you think ?
What is the interaction between manual controls and DAC controls? Suppose pot is set "low" and DAC is set "high" on the scale. What happens, who has priority?
Great question. I depend the tension applied on DAC and the force applied on stick. If pot is set totally "low" and DAC is set totally "high", VOUT_V is set to zero, so pot has win over the DAC.
Essentially you seem to have two unbiased emitter followers driving the pot slider. The emitters won't begin to respond until the base voltages swing at least +/-0.6 volts from the central voltage. What you really need is an op-amp with low output impedance driving the slider, if I understand what you are trying to achieve.
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