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RCFS-V2: New FailSafe with Glitch Filtering.

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but then i wont be able to use low voltage detection?

Yes you will. That is the reason for the diode stacking in front of the 5.0V LDO Vreg circuit. Low Voltage alert will occur when the "6V" battery is at about 5.5VDC.

If you use a LDO Vreg, be sure to follow the data sheet. Do not omit the required caps.

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so tell me, should everything work fine now?

kytkenta1jv.th.jpg

would any "normal" diode whit forward voltage of 0.6V, work there, or should forward voltage be bigger?

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If your "6V" power source is a 5-cell NiMH or NiCD then I think you need two series diodes. Any silicon type should work, 1N914, 1N4148, 1N4000, and so on. After it is built, you can optimize the diode count (if necessary).

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Realizing of course that the failsafe timeout value is hard-coded, what would it take to alter the length of time before failsafe activation occurs? I'd like to use this for the failsafe timer in a submarine but 1 sec is less than optimal. 7-10 sec would be preferable.

Regardless of the answer, thanks much for sharing your work!

Kevin McLeod

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You can change the timeout by altering PIC address 185h. Currently this location contains object code for a "SUBLW 2Dh." By increasing the subtract value you can increase the flywheeling time. I believe a FEh would provide about 6 seconds. You'll have to determine the object code for this.

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I am building this project for my monster truck as well. I am using a high torque servo and a 7.2v 1200ni-mh 5-cell hump pack. With the 12f683 PIC only running at 5.0v would the LM7805 voltage regulator work for the drop to the PIC. I am not runing the voltage detection option.

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The LM7805 will not work well with 7.2V battery apps. You need an LDO type Vreg, such as the LM2931 or LM2940. Be sure to include the input/output caps that the mfg's data sheet recommends.

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Update- I just thought I'd take the time to pop in again and say "Thanks a bunch, I've completed my RCFS-V2 and it works great!" FWIW, I initially I changed address 0x185 from 3C2D to 3CFF as recommended but the code never seemed to emerge from "hold" mode. (It's also possible I might not have waited long enough...) Having run into similar things before though I dropped the value to 3CFD, and all became well.

RCCAM_FAILSAFE.JPG

And here's a shot of what my RCFS-V2 is slated to guard, a scratch-built 1/96 scale OSCAR II...

new_appendage_planes27.jpg

Thanks again!

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It's good to hear it worked out. What did the revised delay time turn out to be? BTW, the sub looks like a fun project.

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Circuit works great!!! Only Question I have is when the signal is lost it takes a second or two to make the servo move to its preset value. Is there a way to shorten this delay time?

Edited by bbcmlibu

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You can use the same method that was used in the earlier post to lengthen the time. However, the failsafe is a 2-step process. Last position hold occurs first (during the period you want to shorten), followed by the optional servo preset. Changing the timing to be much shorter is (in my opinion) not the optimal solution.

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Hi!

It's a old topic but I need some help.

I will RCFS in my truck operating with 4.8V. No problem at this point, but sometimes I use Alkaline batterys (6V).

If I use a LM2931 and 4.8V it will work fine? Or I need to remove the LM2931 when using 6V?

Thanks,

Ismael

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It should still work fine if operating on 4.8V while a LM2931 5V LDO Vreg is installed. The only expected issue is that the voltage to the PIC will be reduced by about 0.5V.

However, the problem with dry batteries is that their voltage is allowed to get quite low before they need to be tossed. So, if you let the voltage get too low, things can get goofy.

Long story short, just try it and see.

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It should still work fine if operating on 4.8V while a LM2931 5V LDO Vreg is installed. The only expected issue is that the voltage to the PIC will be reduced by about 0.5V.

However, the problem with dry batteries is that their voltage is allowed to get quite low before they need to be tossed. So, if you let the voltage get too low, things can get goofy.

Long story short, just try it and see.

Hi!

And this solution: http://www.rc-cam.com/forum/index.php?show...post&p=6639

It will work better?

Thanks,

Ismael

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Looks fine to me. It is not better per se, just another way to limit the PIC voltage to 5VDC.

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Hi!

When I turn on the RX before TX, the RCFSv2 does nothing. The RCFS don't detect signail fail. I need to turn on and off the TX for the RCFS detect signal fail.

Is that correct?

[]'s

Ismael

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Why this?

It is not possible to modify the software for when RX turned on without TX, the system detect signail fail and enter in fail safe mode?

[]'s

Ismael

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It's a deliberate feature. It prevents unexpected servo movement until the user is actually prepared to use the R/C system. This trick allows the servo to fully idle and it will draw minimal current with this arrangement. FWIW, it is not recommended to turn on a R/C Rx before the Tx. It's an old golden rule that I think is wise to follow.

What are you doing that requires a servo pulse before the R/C Tx is turned on?

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It's a deliberate feature. It prevents unexpected servo movement until the user is actually prepared to use the R/C system. This trick allows the servo to fully idle and it will draw minimal current with this arrangement. FWIW, it is not recommended to turn on a R/C Rx before the Tx. It's an old golden rule that I think is wise to follow.

What are you doing that requires a servo pulse before the R/C Tx is turned on?

Hi!

I am doing nothing special, just using the system in a auto.

I just think that is a form to know if you have signal or no.

[]'s

Ismael

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