Rear Panel
Other Connectors
In addition to the 20 BNC connectors, there are two 37-way D connectors, a 5 pin circular connector (180 degree locking DIN type) and a 4mm grounding socket.
The circular connector is an alternative bath (or other reference) potential input, and it also has +15V and -15V power supply connections, to allow a powered preamplifier to be used here. The input resistance is 10K ohms, going to a virtual ground. The gain can be reduced by including an appropriate resistance in series, e.g. 90 K ohms if a preamplifier with a gain of x10 is used. Any signal applied here is added to any signal applied at the BNC input.
The first of the two 37 way connectors is a duplicate of all the BNC sockets except the bath potential input. The upper row of 19 pins carries the remaining signals, alternating in a bottom row/top row BNC socket sequence, and going in the same direction along the panel, i.e. I=0 current in, freqgen out, vcommand/100 in, vcommandx10 out, etc.. This corresponds to a pin sequence of 19, 18, 17, 16, etc., using the numbering convention for this connector. All 18 pins in the shorter row (20-37 inclusive) are connected to signal ground.
The other 37 way connector is to allow a computer (or other external equipment) to read and/or set the major controls of the Optopatch. The sequence of connections given below is the sequence in which they appear in a ribbon cable when an IDC (insulation displacement, i.e. the type that presses directly onto the cable) D connector is used, since the various functions are grouped in this way, and the D connector pin numbering is shown in brackets for reference.
| 1 | (1) | +5V out |
| 2 | (20) | 0V out |
| 3 | (2) | Osc frequency out at 1V/KHz (or 0.1V/KHz on the 10-100KHz range) |
| 4 | (21) | Logic high out on the 10-100KHz oscillator range |
| 5 | (3) | 5V out (normal), 0V or >5V, according to type of headstage in use |
| 6 | (22) | Auto component of phase control voltage (for reading only) |
| 7 | (4) | Auto component of GS control voltage (can either read or control) |
| 8 | (23) | Auto component of CM control voltage (can either read or control) |
| 9 | (5) | Filter variable control voltage (can either read or control) |
| 10 | (24) | Lock-in amplifier phase voltage (can either read or control) |
| 11 | (6) | Multiply gain x2 input if logic high |
| 12 | (25) | Multiply gain x5 if high |
| 13 | (7) | Multiply gain x10 if high |
| 14 | (26) | Multiply gain x10 if high (the effects of these four inputs are cumulative) |
| 15 | (8) | Set 10Hz filter range input if high (also overrides any higher range setting) |
| 16 | (27) | Set 100Hz filter range if high (ditto for this and the other ranges) |
| 17 | (9) | Set 1KHz filter range if higH |
| 18 | (28) | Set 10KHz filter range if high (none of these high selects 100KHz) |
| 19 | (10) | Selects computer control of the following switches if high, otherwise reads |
| 20 | (29) | Search mode (on junction potential switch) |
| 21 | (11) | Vclamp |
| 22 | (30) | Iclamp (neither of these two gives I=0) |
| 23 | (12) | Big cell |
| 24 | (31) | Patch (neither of these two gives small cell) |
| 25 | (13) | RC enable off |
| 26 | (32) | RC auto (neither of these gives RC on) |
| 27 | (14) | 10pF |
| 28 | (33) | 100pF (neither of these gives 30pF) |
| 29 | (15) | Cap offset off |
| 30 | (34) | Cap +100% (neither of these gives cap +50%) |
| 31 | (16) | Conductance x1 |
| 32 | (35) | Conductance x0.1 (neither of these gives conductance x0.3) |
| 33 | (17) | Phase off |
| 34 | (36) | Dither (neither of these gives phase on) |
| 35 | (18) | ground |
| 36 | (37) | ground |
| 37 | (19) | ground |
The four signals on connection (not pin) numbers 7-10 inclusive are effectively bi-directional. They provide the signals as described, via a source impedance of about 10K ohms, and if they are to be used as outputs, they should be connected to inputs of 1 Megohm or higher input impedance. In this regard, note that buffered (100 ohm source impedance) outputs of three of these signals, i.e. the series cond, cap and filter frequency control settings, are available on BNC sockets and on the other D connector, so the use of those outputs for monitoring is generally to be preferred. The phase control voltage, which is not available elsewhere, is 0 to 10V for a 0 degree to 180 degree phase shift. (Although 5V gives an exact 90 degree phase shift, the overall voltage relationship is not precisely linear, but it is predictable and therefore capable of linearisation by software.) Alternatively, if these signals are connected to low impedance voltage SOURCES, then the source voltages will de termine these signal levels instead. This allows external control of lock-in amplifier phase, filter variable frequency, and the auto components of the GS and CM control settings.
