ZoneMikel's Blog

Just noting some things that are wrong with the board so far. I’m happy to find these now instead of when i have twenty of these boards in my hands.

1. RC0 has no pull up and lets the circuit turn on when it should not and cannot turn the circuit off since it proves to be a weak ground.  Solution: change to one of the port B pins that have pull up resistors built in. UPDATE port b pin 3 did not work it still stays on. Further research required but this isnt super important, it might be better to use a n channel on the 7805 ground as planned initially. If not here is another method.
2. Same as 1 for the charge pin, so change charge pin and keep on pin to port B
3. ISCP pins are not exactly like pickit 2 programmer, solution change on next version mclr,vdd,vss,pgd,pgc,aux
4. There is no voltage drop from 5v to 2.4-4.2v for the power line of the wireless module
5. There is no 1k resistor between the pic and transmitter tx/rx. Transmitter is cmos level but we need to be sure we are feeding it cmos level not +/-5v
6. Holes were too small drill diameter for holes should be 2.9mm and the circile should be at least 5.3 mm. This is for the holes where the board screws into whatever it attaches to.
7. vias/jumper holes were still to small they get all the copper eaten off when i drill them if i was going to drill them myself the bit i have is .7mm so the whole hole should be about 1.5mm to be able to drill it and still have a circle to solder to.
8. The whole single pot voltage divider idea needs to be examined. I thought I could make a voltage divider with just a variable resistor. I think ill need a resistor before or after the pot. There should be a 10k resistor as rk, that would give us V*1/2 to V voltage range.

Basic notes, just stuff i found through further study that i dont want to forget.

Pin 7 on the wireless module is “reserved” and in the datasheet it says you can leave it disconnected or “can be pulled up by a resistor to vcc”. I dont know why they have it connected to a mcu pin on their diagram in the datasheet

The pic transmits it signal on the 4th pin on the wireless connector on the jinx mcu board, so it transmits on the tx pin. This is common sense but it can sometimes get confusing what is transmitting and what is receiving.

Power Circuit 2

I revised the power circuit to use all N mosfets. I thought I could just not allow the battery or charger to the ground so it would not make the loop needed for current to flow. Unfortunatley I had the indicator lights hooked into the same transistor as the batt / charger, this caused the loop too be made anyway. Then I decided to not allow the 7805 to go to ground using a transistor, this partially worked. The problem with it was even if the 7805 is not connected to ground it still lets a little current flow, barley enough to light a led dimly. So its a better solution but not a perfect one. I guess I’ll have to rework it again.

In the latest power circuit I had the switch switching the gate of the mosfet to ground not to the high of the battery as it should be. Its fixed in the multisim document but not on the ultiboard circuit.

In the rs232 circuit the tx / rx were backwards compared to the ones on the jinx mainboard, also the lights seem to be on all the time and just blink when sending. This is only for plugging directly into the mainboard but it is convenient to have them this way.

For the rcr and rct we need filter caps and an antenna the antenna can be just a straight wire of 170mm length. Also the transmission should be inverted so the transmitter is normally off, it also has to be converted on the receiving end. This is just for rcr/rct which we wont be using in the final design.

The power supply for the transmitter is at 5v which is fine for the rcr/rct but will burn up the expensive transducers that we will be using in the final design. We can get some voltage drop by using diodes. We could use a jumper to switch between the 5v or 4v.

Put diodes and other things on the basic hbridge circuit, look at the latest circuit there was no ultiboard circuit. Its written in the lab notebook though.

Solder the jumpers/headers upright straight to the board dont drill holes or bend the pins at 90 degrees it just makes it more fragile.

If the copper pad is too small around where a pin is to be soldered to the board it will eventually come loose and make a bad connection ! Make the pads big.

On the wireless module connector pin5 is enable if we want to turn off the wireless module with the pic we should control that with the pic, right now its just connected to ground. Also pin 6 is rts it will let us know when the buffer is full and allow us to drop the cts line so it can send the info, as is its just connected to a “busy” light. As far as i can tell no pull up/down is needed on the output from the pic to the wireless. Since we might only set the channel every once in a blue moon we might want to make pin8 (fqset) a manual switch. The website says you cant change the channel anyway but we might be able to, anyway it does not warrant a mcu pin.

Transmit and recieve on the mcu board should be switched since pin3 rx and pin4 tx are swapped with pin3 rx and pin4 tx on the wireless module. The mcu tx pin should go to rx (pin3) on the wireless module and the mcu rx should go to tx(pin4) on the wireless module. We will switch it in software for now … DONT FORGET!

When the motors turn on it draws too much power and the mcu wigs out, the solution is to put a large cap between vdd and ground to reduce the dip. Be sure to include a 100uF cap just after the 7805 on the power circuit. This worked well and eliminated that problem.

The voltage divider part is connected to the +5v from the 7805 and should be connected to the batHV+ instead. I fixed it manually on board but we need to fix it before the boards are made again.

BattHV might be a little to HV for the tiny tamaya motors we are using, maybe some diodes to get a vdrop and reduce junk coming back into the circuit ? We have 8v we want about 3-6v i would think. We want the reduction on the Hbridge module not the power module, this way we still are able to see the exact battery power and maybe use it for other things?