I have been working on improving the hardware design of the dynamic clamp system, especially to make the need for calibration less frequent (and possibly eliminate it entirely).
The main points are that the new hardware design: (1) uses a 3.3 V voltage regulator to provide a reference voltage for the circuits of Figures 2B and 2D rather than relying on the output of the rail splitter for this purpose (the rail splitter continues to provide the ± 9 V needed to power one of the op-amps), and (2) rearranges the resistors so that it is simpler to find values that will capture most of the dynamic range of the amplifier and/or digitizer. The main advantage of these changes is that, by using a stable and (relatively) exact 3.3 V as the reference, imperfections in the 18 V power supply (“wall wart”) and some of the other components don’t matter as much. In fact, the system may not need calibration at all.
I also added protection for the electronic components in case of an accidental over-voltage. The particular accident that motivated this change was someone attaching a dynamic clamp circuit designed for a 10x gain amplifier to a 100x gain amplifier. The system got a voltage 10x larger than it expected and did not respond well to the insult ☹. To prevent such unpleasantness in the future, I added two Schottky diodes and an op amp in front of the Teensy that has as its power rails 3.3 V and GND.
The new designs affect the circuits of Figure 2B (scaling and shifting the signal coming from the patch clamp amplifier before sending it to the Teensy ADC input), Figure 2D (scaling and shifting the Teensy DAC output to match the range of the command input of the amplifier), and Figure 2E (adding the dynamic clamp current command to the existing DAQ system’s current command). Each figure at the bottom of this page links to a CircuitLab simulation — just right click and select “Open link in new tab”.
The resistor values given in Figure 2B are appropriate for someone using 100x gain (resistor R4 = 0 Ω just means use a plain wire to connect those points. In this case, resistor R5 can simply be omitted — transforming the second op-amp into a follower rather than a non-inverting amplifier). Someone using 10x gain would use different resistor values, as I explain in the draft methods document (see below).
The 3.3 V source in the diagrams below comes from a linear voltage regulator (https://bit.ly/2mUEDpm). The soon-to-be-updated Construction page will describe how to hook it up.
At some point — hopefully soon (I write this in September 2019) — I will modify the other parts of this website to reflect these new designs. At the moment, the other parts reflect the designs of the original paper. Here is a link to the current draft of a revised Methods section describing the changes: OneDrive_link_to_draft. Comments are welcome.
And here is a picture of the new system. I built it using a breadboard (https://bit.ly/2m8bJ4E) with screw terminals to which one can connect the BNC outputs, so you don’t have to worry about pulling the wires out of the board