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DRC-FM100-SRM-2 Stop Recorder Module

Installation Notes


This device uses CMOS technology. Please observe static precautions when unpacking and installing the SRM-2. Connect the ground (brown) and power (red) wires before making any other connections.

© 1998 by Chad Conrad and DRC Instruments

Patents Pending

SRM-2 Features:

  • 100% compatible with the VDO Kienzle FM-100 Fleet Management System
  • Enhanced trip logging capability
  • Ends trips automatically, even if vehicle is left running (eg. PTO applications)
  • Does not lose 'long idling' information
  • Can be triggered by any event which generates an electrical output
  • No false stops resulting from long waits in traffic
  • No interference with normal operation of vehicle
  • Rugged design resistant to weather and vibration

Theory of operation

The VDO Fleet Manager 100 on-board computer requires that the vehicle be shut down in order to record the end of a trip leg. This can be undesirable in applications in which the driver leaves the vehicle idling during a service stop, and the service stop is to be recorded. One could simply devise some method of disconnecting the appropriate circuits whenever the vehicle is stopped, but this is problematic: Such a solution results in a loss of valuable idling information for the duration that the FM100 is off, and it may result in too many false stops being recorded.

The FM100-SRM-2 senses an external event, such as the driver's door opening, or a parking brake being set, and then shuts down the FM100 for approximately 24 seconds. It then turns the FM100 back on to record whatever is occurring, such as idling. With the re-arming time set to 18 seconds in the FM100 PC software, the FM100 will always register the end of a trip leg whenever the external event happens. One need only choose an external event that occurs every time a trip leg is to be recorded. We recommend the cab-light switch on the driver's door. The external event can be anything which creates a change from a logical low (ground) condition to a high (+12V) condition, or vice versa. (A signal which is normally low and goes high is known as active high, the reverse is known as active low.) The SRM-2 contains a switch that the installer sets to specify active low or active high.


Step 1

Determine what kind of trigger signal you will be using. (eg. the door switch, etc. These instructions will assume that you are using the signal from the door light switch.) Is this signal active low or active high? In other words, does the signal go to ground when you wish to record a stop, or does the signal go to +12V?

[Active High Event Signal]

To determine this, use a properly grounded test lamp. Be sure there is a good bulb in the cab light, and that all switches that operate the lamp are open (ie. the driver door is closed, the lamp is off). With the test light, probe both sides of the door switch until the lamp lights. Now, open the door so that the cab light comes on. If the test lamp stays lit, the signal is active high, and your test lamp is at the point labelled B in figure 1. You will be connecting the SRM-2 to the other side of the switch; call this point A. If the test lamp goes out when the door opens, the signal is active low, and the test lamp is at point A. See figure 2.

Having determined if the signal is active high or active low, open the DRC-FM100-SRM-2 and set the switch to H or L, for active high or active low.

[Active Low Event Signal]

Step 2

Determine if the isolating diode is to be installed. (See below.)

Using the door light switch, you will trigger a trip record every time the door is opened. In some vehicles, there are two switches that share the same circuit (eg. a switch in the cab and the switch on the door). In these circumstances, a trip record may be triggered every time the driver uses the auxiliary switch to turn the light on. Note that in some vehicles the switches are isolated from each other so that this does not occur. You may wish to use a logic probe at point A (figures 1 and 2) to determine if the auxiliary switch affects point A. If it does, and if this behaviour is not desired, you must install the provided isolating diode in series (ie. you will be cutting the wire) with the door switch, as indicated in figures 3 and 4. If you will not be using the isolating diode, then omit it (do not cut the wire). The bent lead of the device is the negative lead (see figures 3 and 4).

[SRM-2 in active high application]

[SRM-2 in active low application]

Step 3

Install the FM100-SRM-2 as indicated in figures 3 and 4, according to the appropriate situation (active high or low). Be sure to connect the ground and constant power lines before any other connections.

Step 4

In the FM100 software, set the arming time for the vehicle to 18 seconds. The FM100 must "log out" the current driver and rearm itself for a trip record to be generated. See figure 5. (The FM100-SRM-2 is set to turn the FM100 "off" for about 24 seconds.)

[Setting the arming time to 18 seconds]

Step 5

Instruct the client/driver: If maintaining the correct driver ID is important to the client, instruct them that they must leave the blue key in the port whenever the vehicle is running so that the FM100 will automatically log the driver back in after each interruption. Alternatively, if the FM100 is set to give an alarm when attempting to start the vehicle without a blue key, then the driver can reintroduce his key upon returning to the vehicle every time this alarm sounds.

Application Notes

  • If the driver door is used to trip the SRM-2, then the driver should close the door before turning the ignition key on. In applications where the anti-theft feature of the FM100 is used, turning the key on with the door open will trip the SRM-2, turning the FM100 off and preventing the engine from starting.
  • The SRM has been tested successfully in a variety of environments. It is possible, though not common, that in some installations a very noisy vehicle electrical system could interfere with the operation of the SRM. The most likely symptom of interference is false triggering, ie. the SRM triggers and turns off the FM100 even though the trigger event has not occurred. If the anti-theft feature of the FM100 has been configured, such interference may even prevent the vehicle from starting, as the FM100 is shut down before the engine has a chance to start. A potential source of this interference is through the RPM line on a gasoline engine where the RPM signal has been taken from the distributor. In such applications, the problem causing the electrical noise should be diagnosed and rectified, as such noise can damage other electronic components in the vehicle, such as the ECM. If the problem can not be rectified, it may be necessary to install a magnetic pickup for the RPM. (A pulse adapter or amplifier may be necessary to use a magnetic sensor with the FM100.)
  • The 18 second arming delay set in step 4 means that the driver must start the vehicle within 18 seconds of inserting his blue key. This should not be a problem, as manufacturers do not recommend cranking a starter motor for more than 15 seconds at a time.
  • In order for the FM100 to properly automatically log the driver back in after a stop induced by the SRM-2, it is preferable for the driver to leave his blue key in the port all of the time that the vehicle is running. Alternatively, he can reintroduce it upon returning to the vehicle, but the idle time during the stop will be recorded under an unidentified driver ID. Note also that an RPM signal must be present for the FM100 to automatically log a driver back on when the SRM-2 turns the FM100 back on. If an RPM signal is not present, this function will not work.
  • The SRM-2 uses CMOS technology. Please observe static precautions when unpacking and installing the unit. Connect the ground and power wires to the module before making any other connections.


Size: 33mm 89mm 64mm
Weight: 170g
Length of leads: approx 25cm
Voltage: 12VDC, negative ground
Current draw (at 12.5V):
     at rest: 9mA
     triggered: 36mA
Operating temperature: -40°C to 85°C
Storage temperature: -65°C to 150°C

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Copyright © 1997, 1998 Chad Conrad and DRC Instruments ALL RIGHTS RESERVED