Anyone have a link to a schematic diagram for the Victor 884 speed controllers?
Can the PWM input handle more than 5 volts? I have a circuit that I want to use to control the Victor but the PWM signal is around 8 volts or so. I am interested in the input section limits.
-Hugh
Although this doesn’t answer your question directly, you can use a 5.1 volt Zener diode (and a low-value series resistor) to clamp the input voltage to 5 volts or so.
Does the signal itself go to 8 volts, or do you just have 8 volts on the “power” wire? If you just have 8 volts on the “power” wire, it doesn’t matter because it doesn’t actually hook up to anything in the victor.
On another note, I am curious what circuit you want to use and what you would accomplish by using it.
If the Victor PWM input is the optically-isolated connection I think it is, limiting voltage is not as important as limiting current. Don’s suggestion of a zener diode with a series resistor is fine, but it’s very likely that a simple series resistor alone will be all that is necessary.
Determining the appropriate value of that resistor is a separate matter. That’s where it would be nice to have a schematic, or at least a specification of what the Victor’s typical PWM input current is. As a ballpark guess, for an 8 volt input I would try starting at about 1 kilohm, then reducing the value if necessary until I got consistently correct operation.
This is the CAN forum. Are you making a PWM device to make Victor 884s work with Controller Area Networks? I’m confused.
Thank you for your ideas.
I am sorry this is in the wrong place. I intended it to go in the electrical section, but I got sidetracked looking at CAN, then forgot to go up one level before posting.
We are making a tester that our mechanical guys can use during the proto type design phase. They often want to run a motor to test some mechanism and have not had a good way to do that. Typically they would just connect it to the battery, but that gives them a false sense of power that is not really available when being controlled by the robot, because the battery is not very current limited. Or we would connect it to a control system, which is not very convenient.
The circuit is this device:
http://gadgetgangster.com/find-a-project/56?projectnum=206
On a scope the signal looks just like the output from an IFI RC controller except for the voltage. With an 8 volt power supply the open circuit voltage is 8 volts, but connected to a victor it drops to 1 volt.
The Jaguar schematic shows an input to an optical isolator, which would be easy to interface to like Alan said using a series resistor. I would like to be able to use either a Jaguar or a Victor,
I would still like to find a schematic diagram for a Victor 884.
Thanks.
-Hugh
My understanding is that the Victors take more current to control than typical PWM controllers can source, which would explain exactly what you are seeing. I remember IFI selling “converters” that probably just amplify the current that the speed controller can draw from the PWM line. You can easily create a buffer with an op-amp and a 5 volt supply voltage. I also bet there are other chips that some of the other guys can point you to that also will “amplify” the signal.
Hugh,
Are you saying you connected it to a Victor and it didn’t work? The assembly instructions show the circuit connected to a Futaba 4.8 volt battery pack. It should produce standard RC remote signals that the Victor can use. Remember that if you are looking at the low side of the opto coupler then the voltage you see with a scope is the 5 volt supply less the drop across the diode and the series resistor. Remember that the Victor PWM input has a signal pin (White), a power supply pin(Red) and common pin (black). You must supply all three between the circuit and the Victor. There is the possibility you have damaged the Victor using the higher voltage. Try hanging a resistor of say 10K across the signal output and common (-) and then check with a scope. It should swing between power supply and zero volts.
The simplest way to take care of this would be to just use a ~5 volt source to power the servo tester. Unless you have 5 volt source, the easiest way of getting 5 volts would by using a lm7805, $1.59 at RadioShack. Connect the left most pin to the power supply, the middle to ground, and the right one to the voltage input on the servo tester.
Better yet, if you haven’t already bought the servo tester, find one with a regulated 5 volt supply or just make one yourself, it can be a great learning experience. There are many circuit diagrams for servo testers online (and probably even a few on Chief Delphi) that are based on the 555 timer chip (the same as the servo tester you linked to).
IFI has not released schematics for their products. They do answer questions on their support forum.
It turns out the 10K pull-up resistor on the output of the NPN transistor limits the current below what the speed controller requires.
The solution was very simple. Changed the 10k value at R1 to 1.2k and now the circuit drives either a Victor or a Jaguar just fine.
Thank you for all your comments and help.