# adjustable voltage controlled current source with negative values

I have a MEMS mirror which can tilt based on the input current. The current can vary between -15mA to +15mA in order to change the angle of the mirror from -15 to +15 degree. Now, I need to have an adjustable voltage-controlled current source that can also provide negative values. I prefer to use Raspberry pi or Arduino. I appreciate any help.

• Are you sure? Not entirely sure what your device looks like, but is it some form of voice-coil actuator? And if so, what's the coil resistance? It may be that you are better off to simply do voltage mode control, since at sufficiently low frequencies the coil is just a resistor. – Jeff McBride Apr 24 at 16:24
• It's a Hamamatsu MEMs coil – Sunnyskyguy EE75 Apr 24 at 16:25
• Also, do you need to care about how quickly the mirror settles into its new position, or are you ok to simply adjust the current and wait for the mechanical system to settle? I know in some such actuators (e.g. the auto-focus voice-coil on cell phone cameras) there is a compensated step function, tuned based on the resonant frequency of the spring/mass system, to minimize settling time. – Jeff McBride Apr 24 at 16:26
• Resonant frequency is around 500 Hz but rated from DC to 100Hz – Sunnyskyguy EE75 Apr 24 at 16:32
• If it's like this: hamamatsu.com/resources/pdf/ssd/s12237-03p_koth1006e.pdf, the resistance is pretty large (~165 ohm), so to get 15mA you would need around 2.5V. I would think your best bet is to control with voltage; you may even be able to control with a PWM duty cycle. If you want 10mA, you would need a voltage of 0.1 * R (165) = 1.65V. For 3.3V drive signal, you would need a PWM duty cycle of 1.65/3.3 = 50%. To get a negative current you could use an H-bridge. – Jeff McBride Apr 24 at 16:33