Raspberry Jam (RJAM-U) Universal Digitizer



All models of Raspberry Shake, including the RS1D, RS3D, RS4D, RBOOM, RS&BOOM, RJAM and RJAM-U 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-U) Technical Specifications Sheet


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

For details on the RJAM-U’s instrument response, see: rjamresponse-universal

RJAM versus RJAM-U

The RJAM-U replaced the RJAM in late 2020 as a more universal and turn-key solution. It is no longer necessary to calculate any resistor values / solder any resistors or capacitors on the front-end of the RJAM-U board. All gain selection is now done via firmware using the http://rs.local web front-end.

The RJAM-U is a ‘universal’ input solution that will accept any active input. It also has provisions for connecting a passive sensor (geophone) directly.

Similaritiies to the RJAM, the RJAM-U has:

  • a 50 Hz Low-pass filter
  • an anti-aliasing filter
  • the same 24-bit ADC
  • a 3-channels output at 100 sps
  • inputs that are protected against over-voltage
  • inputs that are protected against ESD
  • a place available for a ‘damping’ resistor to be soldered in
  • the same board size
  • operation is the same as all other Raspberry Shake boards (data is delivered as normal)

Differences to the RJAM include,

  • No resistors need to be calculated or soldering in except perhaps a damping resistor (in the case of passive sensors)
  • Gain configuration now done as part of web front end (http://rs.local)
  • If a damping resistor is needed, no odd calculations are needed. Only those normally done by anyone adding a damping resistor to a geophone when the manufacturer hasn’t given the value needed. Normally, enough information is given by the manufacturer to make this a trivial calculation.
  • No capacitors need be calculated or soldered in. The 50 Hz low pass filter will always be at 50 Hz.

Design and Gain Selection

The RJAM-U 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. Though, with single-ended inputs, one loses half the dynamic range.

The desired gain can be adjusted through the http://rs.local web front end. The system is highly customizable for any sensor that has an output between +/-0.15 Volt to +/-10 Volt referenced to ground (termed 0.6 Volt differential to 40 Volt differential).

Configuration options include the following input ranges and their corresponding differentials:

Input Range Differential (V)*
+/- 0.15V 0.6 V
+/- 0.75V 3 V
+/- 1.0V 4 V
+/- 1.5V 6 V
+/- 5V 20 V
+/- 10V 40 V

(*) To within 1-2%

The configuration can be changed any time by the user without worrying about damaging the board. Incorrect configuration will not damage the board.

Active sensor configuration is simply selectig the proper input range at the http://rs.local web front-end. +/-5 and +/-10V differential inputs will cover most active sensors in seismology. By far the most common passive and active output level is +/-10 V (40 V Differential). There are a couple odd balls out there in the seismic world.

Passive sensor configuration is based solely o the geophone’s sensitivity (generator constant). This is done by assumng a 26 mm/s maximum motion ad then calculatiing the maximum output expected. This is a simple calculation with no special cases. Then, depending on what maximum output is expected, an appropriate gain selection is chosen for the RJAM-U. Incorrect selections will not harm anything.

If the output level of your sensor is not one of the above listed values, the RJAM-U’s dynamic range may be reduced. For example, if a 0 to 5V (‘single ended’) output sensor is used, then the usable dynamic range is reduced by 1/2. The same would be true for other modern digitizers like the Earthdata 209. In order to calculate the loss of dynamic range loss in %, subtract the RJAM-U’s input range from the sensor’s output in Volts, divide by the RJAM-U’s input range and multiply by 100. E.g.,

Sensor output: +/-9.75V. RJAM-U @ +/-10V. Dynamic range loss: (10-9.75)/10 = 2.5%


The RJAM-U 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-U 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.


Passive Sensors

Examples of passive sensors that RJAM-U is compatible with:

Any passive geophone can be hooked up to the RJAM-U. However, as passive geophones have a plethora of different sensitivities, it is impossible to say whether or not the full dynamic range of the RJAM-U can be used. Basically, if the result of multiplying the geophone’s sensitivity by 26mm/s gives one of the Differential voltages listed in the table above, then the full dynamic range can be used.


Low sensitivity sensors not directly supported, though some will match up with the RJAM-U’s input ranges quite well. For best results with small geophones with sensitivities < 55 V/m/s, use the RS1D or RS3D.

Manufacturer Sensor Notes
Many Geophones WARNING: We do not recommend the RJAM-U for small, low generator constant (e.g., 28.8 V/m/s) geophones. Use the RS1D or RS3D instead.
Kinemetrics SS-1 Ranger  
Sercel L-4C previously Mark Products
Teledyne Geotech




School seismometers AS-1, EQ-1, TC-1 Classic slinky and gaden-gate style classroom seismometers

A comment on damping resistors:

Damping resistors change the response of the geophone, independent of any attached digitizer. For the RJAM-U, the value of the damping resistor needed is not affected by the input structure of the digitizer. Stated another way, with the design of the RJAM-U you do not need to take the digitizer into account when determining a damping resistor’s value. Thus, for the RJAM-U, the user can use the expected or geophone manufacturer suggested damping resistor values. Please consult the manufacturer’s data sheet in order to determine the appropriate value for any necessary damping resistors.

If you need a damping resistor, we have left a place on the RJAM-U board for this. The resistor will have to be a SMD part (a big package: 0805).0805 was chosen so that customers could easily solder the resistor if needed. Generally, though, we do not recommend soldernig damping resistors to the RJAM-U board. It would be best practice to solder any damping resistor onto the geophone or at the board’s input pads.

Active sensors

The RJAM-U 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)



See above “Recommended component values for active sensors with 10V Differential outputs - Episensor FBA ES-T specific”


See above “Recommended component values for active sensors with 10V Differential outputs - FBA23 specific”


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.

RJAM Cable diagram and connector specifications

Raspberry Jam Universal Digitizer (RJAM) Cable Diagram Sheet

The RJAM-U DIY solution ships with a 9-pin male connector as shown below:


The female counterpart can be purchased on Digikey:

Contacts: Digikey WM2512-ND

Connector body: Digikey 23-0050579009-ND

Hand crimp tool: Molex 0638111000 (Digikey WM9999-ND) or equivalent

The sensor inputs (Z, N, E with +, -, and Ground) are shown on the back of the board underthe 9-pin connector as seen in the image below. The image is included here for reference in case your header covers up the labels.


The RJAM-U 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.