need your opinion for my project - Page 1
Forum section: electronics / beginners

author: Darius85
author_rank: Newbie
timestamp: February 15, 2021, 11:42:03 pm
content: Hi EE's my name is Jordan and i'm new in the field! I want to build a rf analog remote control for a boat and i need your opinion on it! Thank you in advance

author: Darius85
author_rank: Newbie
timestamp: February 15, 2021, 11:58:33 pm
content: Forgot to mention that this is only the transmitter part

author: penfold
author_rank: Frequent Contributor
timestamp: February 16, 2021, 01:38:37 am
content: Hi,Welcome!My only significant point to make is about the LEDs, each one needs to be wired through its own resistor to ground, and depending on the specific LED voltage drop, that resistor is going to be a lot lower than 100k, maybe 220ohm ballpark.The resistors R1 and R2 look suspiciously high, but they depend on what the resistance of the input potentiometer is and I don't know what that is. Everything else around the opamps looks "calculated" so I'm guessing you've chosen them specifically to set the min/max frequency. I don't know anything about that transmitter module, but its shouting for a couple more decoupling caps in parallel with the 10uF (maybe 100nF and 10nF) to my instinct.Dan

author: srb1954
author_rank: Super Contributor
timestamp: February 16, 2021, 07:05:13 am
content: Quote from: Darius85 on February 15, 2021, 11:42:03 pmThe circuitry for the joystick inputs is very strange. Is the joystick a continuously adjustable analog joystick or is it a switch type joystick?If the joystick is the analog type then the first 2 op amp stages IC1a and IC1b can be eliminated and the joystick connected directly to the inputs of the window comparator stages IC1c and IC1d. However the use of the LM324 op amp is not recommended here as it can barely supply an adequate output voltage to meet the high logic level required by the transmitter module. Either use a rail-to-rail output op amp or use a comparator IC (LM339) with pull-up resistors.If the joystick is the switch type then the op amps can be eliminated altogether and the inputs, with suitable pull-up resistors can be directly connected to the transmitter module. If you have a problem with contact bounce with the joystick switches then you could use an RC filter on the switch outputs followed by a Schmitt trigger IC (74HC14) to square up the signals and provide proper voltage levels to the transmitter module.The LEDs are superfluous here as the transmitter is configured to transmit continuously. In the application note for this module these diodes are actually ordinary silicon diodes rather than LEDs.

author: ChenBH
author_rank: Newbie
timestamp: February 16, 2021, 02:23:57 pm
content: As been said, it will be best to use a comparator for the window detector part.I come with a question: what is the function of IC2?

author: Darius85
author_rank: Newbie
timestamp: February 16, 2021, 03:04:44 pm
content: Sorry for the lack of info guys! This is a two motor rc boat with two one axis joysticks and 4 button for servo drive! The idea is to send the signals from the 4 comparators to 2 h-bridge drives. I dont have any exerience with arduino and i want the simpliest analog design posible.here is a link to http curcuit simolator with the motor drive!https://tinyurl.com/yybkxoq2

author: Darius85
author_rank: Newbie
timestamp: February 16, 2021, 03:07:01 pm
content: Thank you for the advice! The second one is for the second motor

author: penfold
author_rank: Frequent Contributor
timestamp: February 16, 2021, 03:41:29 pm
content: Do you need the window comparator? The voltage buffer needs to be an opamp, but the Schmitt trigger oscillator would be better with an actual comparator, and could you generate the inverse signal with a standard 74xx series logic inverter? I'm being a bit lazy not looking up the spec of the transmitter module, but it seems like it may be a bad idea to rely on it to carry a "PWM" (is it more like constant off-time variable frequency?) signal, what happens if it loses connection, do all the outputs default to off?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 16, 2021, 03:50:28 pm
content: Apologies if this is stupidbut in your schematic, does X represent no connection (as far as the schematic editor is concerned)? If so, are you planning to use PCB layout software? I think having these connections set up as no connection will be problematic. You should put a component there such as a header pin so that the PCB software will create a solder pad.

author: Darius85
author_rank: Newbie
timestamp: February 16, 2021, 05:09:05 pm
content: Quote from: penfold on February 16, 2021, 03:41:29 pmThe window comparator is for the zero state of the pot! Yes i know for the opamps an comparators but will try with the 324 for now! I gona build a proto before makeing the final bord. Transmitter module is holtek tipe and stop if it loose the signal. The module interface is pararell and my pwm signal is at 270Hz! Hope it can carry it! The transmitter can carry hi state and open state signals or ones and zeros!

author: Darius85
author_rank: Newbie
timestamp: February 16, 2021, 05:26:43 pm
content: Quote from: JohnnyMalaria on February 16, 2021, 03:50:28 pmThe schematic is from Eagle and the X-ses are pads. Yes i will make a pcb for it again with Eagle!

author: penfold
author_rank: Frequent Contributor
timestamp: February 16, 2021, 05:43:25 pm
content: Quote from: Darius85 on February 16, 2021, 05:09:05 pmAhh, I see what you're doing now, I'll confess I wasn't really paying attention to what your window levels were so assumed they were set much closer together than they are, its a good idea, but it does still rely on how well defined the output voltage of the op-amp is - could you use a couple of zeners to provide a more accurate clamp and obviously adjust your timing R and C accordingly?