Skip to content

MS4 Tech Notes

ACC16 Coupler for the Microstimulator System


Product: MS16, MS4
Version: All
Date Added: 2007-03-30


The MS16 and MS4 stimulus isolators may generate a DC bias current (up to 0.2 uAmp in the 100 uAmp range and up to 2 uAmp in the 1 mAmp range) on any stimulation channel even during a quiescent state. While this may not have significant short-term effects, over time, it may cause unintended tissue damage.


This problem primarily affects researchers using electrodes with impedances of more than 100 kOhms.


To resolve this issue, TDT supplies an ACC16 AC coupler (pictured below) with each MS16/MS4.

Each channel of the ACC16 coupler includes an RC circuit with a one microfarad capacitor in parallel with a 1 MOhm resistor. The coupler acts as a 1.6 Hz high pass filter, eliminating the DC bias current. It also acts as a voltage divider, decreasing the voltage and thus the current delivered through the electrode. The actual current delivered through the ACC16 depends on the ratio of the coupler impedance to the impedance of the electrode in use.

To calculate a correction factor for actual current delivered:

  1. Determine the impedance of your stimulating electrode.

  2. Calculate the following equation:

    Correction = 1/(1000000/(ElectrodeImp+1000000))

    Correction = (Electrode Imp +1,000,000)/1,000,000

  3. In your circuit, scale the current output by this value.

    In the example circuit above:

    1. The value for "correction" represents the results of the calculation above.

    2. The value for "amp" represents the desired amplitude of the stimulus signal.

    3. The values for the "Limit" component should be set based on the actual limits of your systems. The MS16 is available in 100 uAmp and 1 milliAmp versions. In either case, when using the ACC16 you will NOT be able to deliver the MAXIMUM current.


      The scale factor for the Float2Int component above is configured for use with the RX7 processor. When using RZ5, use a scale factor of 1.7394e+006.

If an ACC16 was not provided with your MS16/MS4, contact TDT to request one.

Upgrade required for MS16s with serial numbers < 4000


Product: MS4, MS16
Version: < 4000
Date Added: 2007-02-27


The MS16/MS4 has undergone several design changes to improve performance and usability. All stimulus isolators with serial numbers less than 4000 should be upgraded to the latest version. Contact TDT for an RMA to upgrade your current module.

High Voltage LED on the MS4/MS16 flashes regardless of battery voltage when connected to the NC48 Rechargeable Battery


Product: MS4, MS16
Version: MS4 serial numbers < 4008 and MS16 serial numbers < 4015
Date Added: 2007-09-04


When the stimulus isolator (MS4 serial numbers < 4008 and MS16 serial numbers < 4015) is connected to the NC48 Rechargeable Battery, the High Voltage LED on the front panel of the MS4/MS16 will flash constantly, regardless of battery voltage. Because the stimulus isolator was originally designed for use with the HV250 battery pack (±135 V) exclusively, the low voltage indicator is triggered even if the NC48 (±24 V) is at full charge.

MS4/MS16 devices with serial numbers > 4007 are configured at the factory for either the NC48 or HV250 according to the order specification and will indicate low voltage as expected for the configured device.


If using an MS4/MS16 with a NC48 Rechargeable Battery, ignore the low voltage indicator and use a standard voltmeter to periodically test the voltage of the battery.

Stimulator control bits and relay switching bits not working after power up


Product: RX7, MS4, MS16
Version: TBD
Date Added: 2006-09-22


After power up, the stimulus isolator control bits and relay switching control bits do not work.


To restore full functionality, execute a hardware reset on the RX7 using zBusMon.

zBusMon is available on your desktop or on the Start/TDTSys3 menu.

Stimulator ringing on output waveforms


Product: MS4, MS16
Version: < 4000
Date Added: 2006-09-11


The device's onboard microcode has been modified to eliminate ringing on output waveforms.


If you experience this problem, contact TDT for an RMA to upgrade your current module.

Stimulator output is noisy in Open mode


Product: MS4, MS16
Version: Serial Numbers < 3000
Date Added: 2006-05-31


In some MS4/MS16 modules noise on outputs is high when the output is in 'Open" mode. The noise is especially evident during recording and stimulation events.


Recent modifications to the stimulus isolator resolved this issue. Contact TDT for an RMA for upgrade of your current device.