A simple OpAmp circuit to combine voltage signals coming from different Thorlabs PM2101 photomultipliers+amplifiers system (https://www.thorlabs.com/thorproduct.cfm?partnumber=PMT2101/M)

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C1, C22CP Small 100µf Polarized capacitor, small symbol Radial D10.0mm P5.00mmPanasonicECA-1CM101NichiconUPS1E101MEDP5138-ND519-4059
J11Barrel Jack MountingPin DC with a mounting pin BarrelJack HorizontalCUI devicesPJ-037AWuerth electronic694106301002CP-037A-ND122-4879
J2, J3, J43coaxial connector (BNC) BNC Amphenol B6252HB-NPP3G-50 HorizontalAmphenol031-5431-10RFXARF1690-ND144-0890
R1, R2, R5, R3, R45R 10k Resistor Axial DIN0414 L11.9mm D4.5mm P20.32mm HorizontalStackpole electronicsRNF14FTD10K0TE connectivityLR1F10KRNF14FTD10K0CT-ND125-1164
R7, R62R 1k Resistor Axial DIN0414 L11.9mm D4.5mm P20.32mm HorizontalStackpole electronicsRNF14FTD1K00TE connectivityLR1F1K0RNF14FTD1K00CT-ND125-1159
SW1, SW22SW SPDT in1 on/off Switch, single pole double throw TO-3P-3 VerticalCW industriesGRS-4012-0026Carling technologiesLRR112-2B-JNSW304-ND881-1530
U11LM324 Low-Power, Quad-Operational Amplifiers, DIP-14/SOIC-14/SSOP-14 DIP-14 W7.62mm SocketTexas instrumentsLM324NE3Texas instrumentsLM324N/NOPB296-27903-5-ND197-7250
U1A1DIP Socket 14 pinAssman componentsA 14-LC-TTAE9989-ND674-2438


Hi! Welcome to the PMT-combiner repository.

This project got started when there was the need to combine the signals coming out of two photo multiplier tubes (PMTs) installed in one of the 2-photon microscopes at the microscopy unit in Sussex Neuroscience.

The particular PMTs installed were models PM2101 from Thorlabs. This means that they are actually a "combo" of PMT plus current to voltage converter, and the output signal from the unit is voltage.

Having to combine two voltage signals together, we implemented a simple system with two Operational amplifiers. The first one combines the two voltage signals, but because we didn't want to amplify the signal, this opamp is used in a signal inverting configuration. After this first stage, the signal is combined, but also inverted, so a second stage is used to invert the signal again.

The whole system is powered up with 12 volts, which makes it suitable for battery driven applications. The power signal is split into +-6V as the PMT units output +- voltage as well.

Each channel has a switch which connects the PMT signal to the combining circuitry. If the combination is not needed, the switch can be turned so that ground is connected to the circuitry, allowing for just one PMT to be used at a time.

we are making use of the excellent KitSpace system, head over here and use their 1-click-bom system to quickly get a shopping cart with all the necessary bits to reproduce this board!

Create an issue or drop us a line!