Windows to PIC Interface - (Hexapod Part 6)

The full source code can be found here.

Servo Control

I've now 'closed the loop' for communications with the PIC. Each servo has a pair of scroll bars. One showing the desired position, the other showing the actual. There are two reason why a servo may not be in the desired position.

The first is that the servo's calibration may not allow it to move to that position. If the user selects position 255 and the maximum position the servo can move to is 250 the 'Actual' position will show this. Thats the easy one. The more difficult scenario is that the servo is 'stuck' against something I.E. during a leg movement the leg has come up against an obstacle.

Each servos current will be monitored. If the current exceeds a preset limit (probably around 100ma) the servo will be considered stuck. The PIC will then back the servo off until the current becomes acceptable (probably around 50ma). Neither of these scenarios are implemented in the firmware yet but the UI has allowed for it.

The windows UI has a timer, currently set to 1 second. Each tick of the timer a single byte packet (0x02) is sent to the PIC. The PIC responds with a position packet, which consists of 4 bytes. The first byte is 'A' (0x41). This indicates the following 3 bytes will be the position of the three servos attached to this PIC. The UI receives these bytes and displays them on the scroll bar associated with the each servo. This is for the 'Actual' position.

When the user moves the 'Desired' position scroll bar the UI sends a packet to the PIC which consists of 3 bytes. The first byte (0x01) indicates this is a positioning packet. The second byte indicates which servo should be positioned and the third byte indicates the position it should be moved to.

Request: 02            - UI to PIC, Send Positions
Answer: 41 7F A0 A0    - PIC to UI, Positions are 0x7F, 0xA0 and 0xA0
Request:01 00 17       - UI to PIC, Set servo 0 to position 0x17
02                     - UI to PIC, Send Positions
Answer: 41 17 A0 A0    - PIC to UI, Positions are 0x17, 0xA0 and 0xA0
Request: 01 00 11      - UI to PIC, Set servo 0 to position 0x11
02                     - UI to PIC, Send Positions
Answer: 41 11 A0 A0    - PIC to UI, Positions are 0x11, 0xA0 and 0xA0

Under some circumstances (yet to be determined) the PIC stops responding. It is still holding the servo in position so it hasn't 'locked up' but it seems to have got out of whack somewhere. That'll be the next challenge.

After thats resolved I'll be looking at hooking the current measuring shunts up to the A/D converter and sensing overload situations.

NOTE: Big lesson learned while trying to get the RS232 interface going (specifically the PIC receiving data) don't use hyperterminal. Not sure what it was doing but after trying everything I could think of in the PIC firmware I tried using a different terminal tool and everything started working. So, if your considering using hyperterm, don't, just don't.

First Inspection of the Season - Hive Two

Hive Two is my original hive and has always been very strong. They came through winter very well, considering I haven't touched them for at least 4 months (maybe thats why they come through so well...?)

There was very little dross on the base board and only 6 frames that had any significant rouge comb on. While inspecting the bottom box I came across brood on the 3rd frame in (from the sunny side) but no evidence of recent queen activity down there. There were also a couple of frames that looked like they were almost ready to be capped which is also very impressive for this time of year.

I inserted a drone frame as part of my varroa control strategy. This is earlier than I though I'd be able to but as there were plenty of drones around already I decided to give it a go. In my next inspection I'll try to move the queen into the bottom box and place a queen excluder on to keep her there. This will keep the brood contained and limit the mites options.

Brood, lots of it

The second box, which is full depth as is is the first), also had good honey and pollen stores. There were several frames with significant numbers of eggs so the queen is obviously healthy and active. There were also two sides fully covered by brood.

The third box is a three quarter and had some nectar but nothing else of interest.

Removing center of base board

Varroa seems to be non existent in this hive at present, which is very encouraging. I had expected to have to treat. I've only visually inspected for varroa by breaking open drone brood and eyeballing the workers so there could still be a significant population.

The finished baseboard

My local hardware store sells 3mm galvinised mesh so I bought a piece, but the center out of my bottom board and replaced it with the mesh. This will make monitoring the varroa population much simpler as I won't have to disturb the bees to do it. It also means that any mites that fall of the bees (or are groomed off) will fall out of the hive and not be able to climb onto another bee.

PIC to Windows Interface - (Hexapod Part 5)

The full source code can be found here.

One of the tasks I wanted to achieve fairly early in the piece was the communication between the PC and the PIC. This is fairly simple with any of the PICs that have a USART built in. In fact its trivial. Just configure the port and send a byte. Once its sent, send the next byte.

The following code initialises the USART to asynchronous mode, 9.6kbps

movlw B'10100100' ;initialize USART
movwf TXSTA ;8-bit, Async, High Speed
movlw .25
movwf SPBRG ;9.6kbaud @ 4MHz

movlw B'10010000' ;bit7 = SPEN, bit4 = RX Enable
movwf RCSTA

Sending the data is then simply load the byte into the TX register and wait for it to be sent

SendPositions:

;continuously send servo positions to PC

btfss SEND_STATUS, 0    ;wait until the interrupt changes something
goto $-2
BCF SEND_STATUS, 0      ;reset the 'something changed' flag

movlw "A" ;A means the next 3 bytes are servo positions
movwf TXREG ;next line
btfss TXSTA,TRMT ;wait for data TX
goto $-2

movf SERVO0POS, w ;move data into TXREG
movwf TXREG ;next line
btfss TXSTA,TRMT ;wait for data TX
goto $-2

movf SERVO1POS, w
movwf TXREG ;next line
btfss TXSTA,TRMT ;wait for data TX
goto $-2

movf SERVO2POS, w
movwf TXREG ;next line
btfss TXSTA,TRMT ;wait for data TX
goto $-2

goto SendPositions

The above code sends the ServoPosition packet to the PC. The servo position packet is identified by the first byte being an 'A'. This is just a character I chose at random, 'A' seems like a good place to start. When the software on the PC sees an 'A' it knows the next 3 bytes will be the positions of the 3 servo connected to the PIC.

The PC software, written in C#, opens the serial port and listens to all bytes coming in. These bytes are fed into a packet factory that looks for the 'A' character. When this character is seen it records the next 3 bytes and then creates a "ServoPosition" packet. This packet is then sent, via an event to anything that is listening, in this case a windows form.

The form outputs the data in two forms, a graphical form and a textual form. The software on the PIC current decrements the servos positions each time the interrupt runs so the servos are constantly moving through their full range. The next step is to set the PIC up to receive data from the PC and allow the user to move the scroll bars to position the servos.