Need quiescent current for XY-MK-5V 433Mhz Rf receiver

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
So I wanted to make an RC car without using an arduino microcontroller. So I have bought HT12 Encoders and Decoders as well as these RF Modules (https://www.amazon.com/UCEC-XY-MK-5V-Transmitter-Receiver-Raspberry/dp/B017AYH5G0). The problem is that the receiver doesn't work properly when there is a load such as a motor. My questions is how to get Static Current for the receiver to work properly even if there are two motors running.

I have used many capacitors in parallel to the power supply to smooth out voltage drop when both motors run, which helps a lot but it's still far from perfect. The receiver still takes awhile to get up and running properly in order to receive information. In some cases it might take a 2-3 seconds for the receiver to start working maybe 5.

I use an L293D to drive the motors and there are PNP transistors since the Decoder outputs one when no buttons are pressed. In this schematic the receiver and L293D are powered individually but the same problem exists.

Sorry in advance for my schematic drawing skills, if you have any advice on that, then it would be greatly appreciated.
RC_Car-6977d9bec891487db3acdf56b066e8e4.png
 

ericgibbs

Joined Jan 29, 2010
8,715
hi DS.
Have you tried a Schottky diode in series with HC12 +V input, decoupled at the HC +v input with say a 22uF at 6v.?
As you may know grounding paths are very important when powering logic and motors from the same source.
I have found also that tying the unused I/O [TXin or RX out] on the HC12 to 0v.
E
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
Do you mean the Decoder? The problem that I think is the receiver module. Because when the motors run, the Decoder's status LED (at pin 17) turns off indicating that there is no data being received, but the transmitter works fine.

So should that same tactic be used for the Receiver?
 
Last edited:

ericgibbs

Joined Jan 29, 2010
8,715
hi David,
Misread your HT12 as HC12, as you may know the HC12 is a transceiver module, sorry about that.

Regarding the in series diode, it is a common way of giving some isolation for the logic supplies from noise etc, generated by motors pulling on the same supply.

E
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
I'm using both RF modules and HT12D and HT12E ICs.

But now i know you meant the RF receiver so I will do what you advised.

So have a diode going in series to Receiver's V in. Then have a capacitor parallel to Receiver's V in and Gnd?
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
So I'm still having some troubles with the receiver and keeping it powered and responsive. Is there anything else I should do? Maybe a constant current source from an LM317? I do have these 5 V regulators, the only problem is the closest I can get to is only 4.9 V.

It's responsive when the motors run for a second, but when driving for awhile it takes a while to get a stable V for the receiver.
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
So I'm still having some troubles with the receiver and keeping it powered and responsive. Is there anything else I should do? Maybe a constant current source from an LM317? I do have these 5 V regulators, the only problem is the closest I can get to is only 4.9 V.

It's responsive when the motors run for a second, but when driving for awhile it takes a while to get a stable V for the receiver.
 

ericgibbs

Joined Jan 29, 2010
8,715
hi D,
As it is an RC car I guess space is a problem for mounting a separate battery for the receiver.?
What is the specification of the car battery.?
I do not see how using a CC source will help prevent power supply voltage pull down when running motors for a while.
Can you measure the actual battery voltage while the motors are driving on load.?
E
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
I am okay with using a separate battery supply. I used my power supply to power the receiver and Decoder at about ~6 V (5.989 V actualls). The diode is the 1N5819 and electrolytic capacitor at 47 microFarads for the filter system. The receiver's Vcc when recorded is ~5.7V. When the motors run the voltage drops to ~5.650 and it takes a while to stabilize.

If the RC car is on the ground but it's better when the motors drive no load (of course) so maybe I should use a different gear system than the one i took apart from a toy.
 

DickCappels

Joined Aug 21, 2008
5,873
One trick I've seen used in a couple of different toy RC cars is to put a ceramic capacitor from each motor lead to the motor case right at the motor. Like in the photo below but with shorter leads. The idea is to keep the RFI inside the motor case and not let it get out through the leads.

upload_2017-8-18_18-40-33.png
 

Thread Starter

David Sumadsad

Joined Aug 12, 2017
9
1503078303157795680682.jpgthe motor i have is like that, the capacitors are 100nF. But in the picture you showed it has a gear system so im guessing that would be another thing to consider150307871950233209750.jpg
Here's the car, nothing amazing looking but it works, it's something simple it only has two wheels one for each side1503079168139869016996.jpg 15030788498852007088426.jpg 15030788951531470503069.jpg
 
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