Raspberry Jam (RJAM) Universal Digitizer



All models of Raspberry Shake, including the RS1D, RS3D, RS4D, RBOOM, RS&BOOM and RJAM use the same software. Sections of the Quick Start Guide have been tailored to each product but the overall manual applies to them all. Other specific manual sections, like this one, have been created to address issues specific to the individual products.

Technical Specifications Documents

Raspberry Jam Universal Digitizer (RJAM) Technical Specifications Sheet


Unlike other Shake products, the RJAM has no long period extension (from 4.5 Hz to ~2 seconds) as this would be undesirable for and incompatible with more sensors.

For details on the RJAM’s instrument response, see: Raspberry Shake RJAM

Design and customization

The RJAM digitizer was designed to work with most seismic sensors and supports 3-channels of single-ended and differential-ended signal inputs, passive and active sensors.

Through-hole mountings are provided for resistors and capacitors to make it easy for electronics engineers and power users/ Do-It-Yourselfers to swap out components. The system is highly customizable. If you prefer the Raspberry Shake to do the customization for you, see: Raspberry Jam Universal Digitizer (RJAM) Customization.


The RJAM board is ESD sensitive, and ESD precautions must be taken when soldering components and hooking up sensors. Even small ESD events can damage the response of the RJAM and cause small signal accuracy or reliability issues, both of which are difficult to detect but cause signal distortion. Also, be sure to populate the card with the appropriate resistors and capacitors BEFORE hooking up any sensors.


Like any digitizer not inside of a metal enclosure, you should be careful with any RF sources in the area.

Channels (as labelled on PCB board):

Channel # Resistors Capacitors
1 R13,R14,R15,R16,R24 C29,C30,C31,C32
2 R22,R34,R35,R37.R38 C23,C24,C58,C59
3 R30,R52,R53,R55,R56 C33,C34,C62,C63

Component Groups:

Group Sensor Type Components
R[damp] Passive with signal output 0 - 3 Volts Damping (“Shunt”) Resistors: R22,R24,R30
R[a] Active/ Passive with signal output >3V R13,R14,R35,R37,R53,R55
R[b] Active/ Passive with signal output >3V R15,R16,R34,R38,R52,R56
C[a] Any, optional LP Filter Capacitors: C23,C29,C31,C33,C59,C63
C[b] Any, optional LP Filter Capacitors: C24,C30,C32,C34,C58,C62


Filter capacitors C[a] and C[b] are optional and can be included to provide, for example, a single-pole low-pass filter at 50 Hz. Filter capacitors were included in board design to provide some minimal protection to keep 50/60 Hz electrical noise out of the system.

Calculation of capacitor values

  1. Cx: C[a] and C[b] are in parallel, meaning their values add.
  2. Rx: R[a] and R[b] are in series, meaning their values add.

So, to calculate the overall frequency response of the input the following calculations are necessary:

  • Low Pass filter resistance value Rin= Rx in parallel with 5.1k Ohm.

  • The input low pass filter is formed with Rin and Cx.

    If R[a] = 33k, R[b] = 12k, C[a] = 0.47u, and C[b] = 0.22uF, then:

    Rx = 45k Ohm;

    Cx = 0.69uF;

    Rin = 45k || 5.1k = 4.58k

    1st LPF -3dB point is: 50 Hz

  • The rest of the input circuitry is formed with, among other effects, an in-series differential LPF. To take this into account, on a first order approximation level, simply subtract about 7dB from the response curve.

  • The response is then the 50 Hz low pass filter followed by the rest of the input circuitry. In this case, this gives an overall -3dB point at about 42 to 43 Hz.

  • The digitizer itself has a response that is -3dB down at 22% of the sample rate. When this is taken into account, the overall frequency response curve can be estimated.

How to determine the value of R[damp] (Passive Sensors only)

A special note on determining the R[damp] resistor:

Passive sensors with outputs in the range of 0 to 3 Volts (e.g., most geophones) only need a damping (“shunt”) resistor (Group R[damp]). To determine the appropriate R[damp] resistor values, you will first have to consult the manufacturer’s data sheet where you should be able to find the recommending damping value. The actual value of the damping resistor used (sometimes called CDR for “critical damping resistor” or just “damping resister” depends on how much damping one wants. The CDR is the maximum allowed to avoid the sensor ‘ringing’ after a step stimulus.

The other resistors in Groups R[a] and R[b] should generally be shorted out (0 Ohm resistor) and the filter capacitors in Groups C[a] and C[b] are optional. If R[a] and R[b] on the RJAM are both shorted (0 ohms), then there will be a parasitic shunt resistance of 10.2 kOhm that appears in parallel to R[damp]. This means that one has to do a parallel resistor calculation to determine the actual R[damp] required. For example, if the geophone data sheet specifies a 1 kOhm damping resistor, the actual value installed for R[damp] should be 1.1 kOhm as 1.1 kOhm in parallel with 10.2 kOhm gives something near 1 kOhm (actually 993 Ohm, but close enough).

If R[a] and R[b] are installed, their resistance value adds to the 10.2 kOhm parasitic resistor. For example, if R[a] = 5 kOhm and R[b] = 0 Ohm, then the “parasitic” shunt resistance is 5k + 5k + 10.2 kOhm = 20.2 kOhm. Now, to get an overall 1 kOhm damping resistance value, R[damp] should be 1.05 kOhm. 1.05 kOhm in parallel to 20.2 kOhm gives 998 ohm (which is close enough to 1 kOhm).

Notice that the higher the value of R[a] and R[b], the less effect they will have on the value of R[damp]. We would not suggest going more then R[a] = 33k and R[b] = 12k, which gives a total parasitic shunt resistance value of 100.2 kOhm. Back to the earlier example, if these values of R[a] and R[b] were installed, and we needed a 1 kOhm damping resistance value for a geophone, then R[damp] could be simply chosen as 1 kOhm, as 1 kOhm in parallel to 100.2 kOhm is 990 Ohm, which is probably close enough to 1 kOhm to be okay.

To help, here is an online resistance calculator: https://ncalculators.com/electronics/parallel-resistor-calculator.htm

To use it, select these settings:

“Find Value of:” R2

“Enter Value of R1:” 10.2 + Z K Ohm

“Enter Value of R2:” —– K Ohm <= this is the value to install at R[damp] on the RJAM.

“Enter Value of Rp:” <desired damping resistor value> K Ohm <= the damping value required by the geophone.

Where Z is the sum of R[a] + R[b] times two (as there are two resistors of each value installed on the RJAM.) If R[a] and R[b] are shorted, the the value for R1 entered above is simply 10.2 K Ohm.

If we use the calculator for the example where a geophone needs a 1 K Ohm damping resistor, and we have shorted out R[a] and R[b] on the RJAM, then the R[damp] value needed is 1.109 K Ohm.


The resistor put in the C[b] position does not significantly affect the value of R[damp] and can be ignored.


Passive Sensors

Examples of passive sensors that RJAM is compatible with:

Manufacturer Sensor Notes
Many Geophones Racotech RGI-20DX has been tested
ASIR A_F2-GS-70  











previously IESE
Sercel L-4C previously Mark Products

Active sensors

The RJAM is compatible with the following active sensors and many more:

Manufacturer Sensor Known* Differential Voltage** Notes

Model [25,25/21]

Model 50

Model 50a

Model 60/64; 60Vx

Model 60UHP


Assuming 40V pk-pk Diff. output; data sheet is inconclusive


Sensor is 44V pk-pk Diff. When used with 40V pk-pk Diff input, signal will clip at ~90% of sensor’s full-scale

36V pk-pk Diff. actual. Use 40V Diff input.

GeoSIG AC-23 20V pk-pk Diff.




S-13 and other passive sensors


Assuming 40 V differential output

Assuming 40 V differential output

See previous table


[3,5T,6,6T,40] Series





Episensor [2,ES-T,ES-U2]

HypoSensors (FBA ES-DH)

SBEPI (202)

We are guessing at what the actual value is, which is 40V Diff input. The +/-5V Diff input is not supported.



Lennartz LE-3D[lite/5s] MKIII 40V input comes close though the dynamic range is reduced. Better would be a 30V input range.







Trillium Compact[PH,AT]

Trillium 120[Q/QA]








RefTek (Trimble)








Assume output is 40V pk-pk Diff., but would be probably better served with a 50V pk-pk Diff. input structure.

Assume output is 40V pk-pk Diff., but would be probably better served with a 50V pk-pk Diff. input structure.

Steckeisen STS[2,2.5,5A,6A] Unsure what output level actually is. Assume output is 40V pk-pk Diff., but would be probably better served with a 50V pk-pk Diff. input structure.

(*) Known = we have tested them in the lab


(**) We assume that, in the seismology world, “40V peak-to-peak differential” output means that the output voltage of each signal line is swinging +/- 10 Volts with respect to ground. We have made this example list with that definition in mind, though it seems that in the seismology world the manufacturers are not consistent with how they specify the output level. In the end, the client is responsible for researching the solution and removing ambiguity surrounding how the manufacturer of their sensor(s) define the output level.


Active sensors must be externally powered.

Cable diagram and connector specifications

Raspberry Jam Universal Digitizer (RJAM) Cable Diagram Sheet

The RJAM turn-key solution ships with an Amphenol PT07A-12-10S female connector. In addition to the sensor and cable, you will need to provide the male counterpart to this connector. We recommend the Amphenol PT06A-12-10P(SR). These are available on Mouser and Digikey. This can be purchased separately at shop.raspberryshake.org.